Endocranium

“ The name cerebrum is also applied to this portion of the brain; frequently, however, the name cerebrum is used as signifying the entire mass of the brain craniad of the rhombencephalon,—therefore including mesencephalon, diencephalon, and telencephalon. The term will here be used as synonymous with telencephalon.
The cerebral hemispheres arise as two lateral outgrowths from the cranial end of the primitive forebrain. They have undergone great increase in size in the course of evolution, so as to form the larger part of the brain ”

“ The thoracic and abdominal viscera were perfectly healthy.
Upon examining the contents of the cranium, the pia mater was considerably inflamed, and an extravasated blotch, about the size of a shilling, was seen upon that membrane, near the middle of the right lobe of the cerebrum. There was no water between the membranes, nor in the ventricles, but a general determination of blood to the contents of the cranium. The medullary substance, when cut into, was full of bloody points. The consistence of the brain was natural. ”

“ After the removal of the brain from the skull the abnormal dimensions of the cerebrum present a remarkable contrast to the normal size of the cerebellum, pons, and medulla oblongata, which also appear flat and broad from pressure. When a horizontal section is made through the hemispheres of the cerebrum and a little above the corpus callosum, the centrum ovale appears unusually large. The cavities of the ventricles are very narrow, their walls touching one another. There is no serum in the pia mater or in the ventricles. The substance of the brain is pale, bloodless, and dry. ”

“ The Cerebrum or Great Brain lies above the plane of the tentorium, and forms much the largest division of the encephalon. It is customary in human anatomy to include under the name of cerebrum, not only the convolutions, the corpora striata, and the optic thalami, developed in the anterior cerebral vesicle, but also the corpora quadrigemina and crura cerebri developed in the mesencephalon or middle cerebral vesicle. The cerebrum is ovoid in shape, and presents superiorly, anteriorly and posteriorly a deep median longitudinal fissure, which subdivides it into two hemispheres. ”

“ There is a respiratory circulation, the contractile ventral vessel which represents the heart sending the colourless blood forward to the respiratory pharynx to be purified. The body-wall is segmented into over fifty myotomes. There are numerous separate nephridia which develop from the mesoderm and open into the atrium. The brain remains undeveloped, being scarcely distinct from the spinal cord. There are two pairs of cerebral nerves, and many spinal, in which the dorsal and ventral roots or nerves do not unite. The sense-organs are simple; there are no paired eyes and no auditory organs. ”

“ On each side there are membranes or skins, which form kinds of ears; and under them others, which at times fill with water, and are then transparent. Under this thick skin there is a cranium, of a kind of coriaceous or cartilaginous matter; and in the cranium we find the brain, which is a white substance, and very firm. At the basis of the head its oval wide mouth is placed, being above two lines long, which often discovers a white hard edge, with which he crops the fucus’s, and other sea-plants, for his nourishment. ”

“ As the fibres of the medulla pass up through the pons to the great inferior ganglion, and the fibres of the corpus striatum pass outward and upward to form the cerebrum, this procession of the fibres is shown in the annexed engraving, in which we see the restiform bodies passing up to form the cerebellum, and the remainder of the medulla fibres passing through the pons, and then, under the name crus cerebri or thigh of the cerebrum, passing through the thalamus and striatum to expand in the left hemisphere of the cerebrum. ”

“ In the same way the thicker membrane which invests the brain is first cartilaginous and then bony, whilst the thinner membrane merely consolidates into the pericranium and integument. In similar order flesh and nerve from soft mucus are confirmed into muscle, tendon, and ligament; the brain and cerebellum are condensed out of a perfectly limpid water into a firm coagulum; for the brain of infants, before the bones of the head have closed, is soft and diffluent, and has no greater consistence than the curd of milk. ”

“ At the same time, the roof of the cranium becomes more and more arched, to allow of the increasing height of the cerebral hemispheres, which is eminently characteristic of man, as well as of that backward extension, beyond the cerebellum, which reaches its maximum in the South American monkeys. So that, at last, in the human skull (Fig. 30) , the cerebral length is between twice and thrice as great as the length of the basicranial axis; the olfactory plane is 20° or 30° on the under side of that axis; the occipital angle, instead of being less than 90°, is as much as 150° or 160° ”

“ The three main divisions of the brain may still be clearly seen from the surface. Posteriorly is situated the hind-brain, now consisting of the medulla oblongata and cerebellum. At the anterior part of the medulla is to be seen the thin roof of the fourth ventricle, and anteriorly to this again the roof becomes thickened to form the rudiment of the cerebellum. In front of the hind-brain lies the mid-brain, the roof of which is formed by the [Pg 294] optic lobes, which are still situated at the front end of the long axis of the embryo. ”

“ The same practice is applied to the serous tissues, but with less success; its proximity to organs eminently putrescible, such as the brain, the lungs, the liver, renders its dissolution more imminent, more difficult to prevent.
“6. Encephalon, spinal marrow, nerves.—We have already spoken of the property of nitric acid, to give consistency to the nerves, without causing them to lose any thing of their pearly whiteness. Anatomists generally avail themselves, for the preservation of the whole nervous system, of the alcoholic solution of corrosive sublimate. ”

“ The oesophagus runs forward to the proventriculus (3) . From this the intestine (20) passes posteriorly.
The brain lies upon the neural side of the endosternite, and the ventral cord (22) passes back through the occipital ring. The neural nerves are cut off, but the left haemal nerves and those from the fore-brain (12) are represented entire.
The first pair of neural nerves go to the chelicerae. The second to sixth pairs go to the next five cephalothoracic appendages, which are represented by the entocoxites (6) . ”

“ Considered in relation to the brain, the membranes, the inner table, and the diploë itself, the outer table presents no other definite organization beyond that of an irregular envelope, which is in some places as thin as a wafer, in others thicker than all the rest of the cranium. But, if we view it from without, we find that every particle of its surface is adapted to some purpose which it has to answer in combination with the soft parts with which it is in contact. Many processes are levers for the muscles ”

“ The cause of such a transformation in a previously entirely normal woman has been found to be a tumor of the adrenal cortex.
But not only is sexuality, and the conduct of the secondary sex characters, connected with the adventures of the adrenal cortex. The development of the master tissues of the body, the brain, the pride and darling of evolution, is in some subtle way correlated with it. The adrenal cortex contains more of the phosphorus-containing substances of the general nature of those found in the central nervous system than any other gland or non-nervous tissues in the body. ”

“ The serous system varies also, though less than the preceding. 1st. Each membrane has its peculiar structure. Compare for example, the arachnoides and the peritoneum; the one fine, delicate and transparent, yields to the least effort, has no resistance, tears almost as soon as it is touched, never remains whole at the base of the cranium, where it is free, if the brain is raised ever so little, and has, when pressed between the fingers, a remarkable softness. The other, thicker and more compact, bears without breaking all the efforts imparted to the abdominal viscera ”

“ In the normal condition it is loosely attached to the brain, from which it can be stripped off without loss of substance. The meshes of the pia, together with the ventricles, constitute a series of cavities connected with each other, containing a variable amount of cerebro-spinal fluid, and they communicate with the lymph-spaces surrounding the blood-vessels. Pressure within the cranial cavity, from congestion of the vessels or from the products of inflammation, is thus relieved in a measure by displacement of the cerebro-spinal fluid, which is driven out through the perivascular lymph-spaces. ”

“ Its cavity is known as the third ventricle. Just craniad of the [343] ’tween-brain, in the median line, is a deep fissure, showing that here in reality is the termination of the original tube, the further extension craniad being due to the pushing forward of the lateral outgrowths, or cerebral hemispheres, which extend in ventral view a considerable distance further craniad. The hemispheres lie also caudad, laterad, and dorsad of the midbrain and ’tween-brain, so that these parts are almost enveloped by the hemispheres. ”

“ Beyond an increase in size, which it shares with nearly all parts of the embryo, and the change of position which has already been referred to, the mid-brain undergoes no great alterations during the third day. Its sides will ultimately become developed into the corpora bigemina or optic lobes, its floor will form the crura cerebri, and its cavity will be reduced to the narrow canal known as the iter a tertio ad quartum ventriculum and two diverticula leading from this into the optic lobes. ”

“ During human intrauterine life the adrenal glands are large and conspicuous, in the first half of the second month being twice as large as the kidneys. Most of this relatively huge size, which happens in the human alone, and not in other animals, is due to enlargement of the cortex. Should this preponderance of the cortex over the medullary portion not occur in the human, that is, if the proportions remain like those of other animals, the brain fails to develop properly, or an entirely brainless monster is generated. ”

“ In more advanced cases, thin patches of lymph, or more extensive strata of it, cover the arachnoid and the inner surface of the dura mater; a puriform fluid is found effused between these membranes, and sometimes blood and matter are deposited in some part of the cerebral substance; bloody serum is effused into the cavities, and at the base of the brain. The above symptoms and appearances sometimes follow injuries not at first thought severe, but are most frequently the result of such as are attended with læsion of the bone, or of the internal parts. ”

“ The lesion fades away gradually so that it fails to involve the temporal convolutions.
The cerebral tissue cuts firmly and smoothly. The tissue of the frontal region is a little edematous. The white matter is of a normal appearance. The ependyma of all the ventricles is somewhat sanded. The fourth ventricle is most affected.
The cerebellum is not edematous and is as firm as the normal olivary bodies. The cerebellar hemispheres are symmetrical and of a normal appearance, save that the laminæ are slightly narrower than usual and very compactly set. ”

“ In all Craniates the dorsally-placed and tubular central nervous system has its anterior portion enlarged and otherwise modified to form a "brain," while the remaining portion, retaining a simpler and more uniform structure, forms the spinal cord. In the embryo the brain always consists of three successive sac-like enlargements known as the fore-, mid-, and hind-brain, and from {144}these are developed the various parts of the complex adult brain, which in the disposition and mutual relations of its parts conforms to a common plan in all the members of the group. ”

“ The circumference of the cranium is 34.5 cm., sagittal diameter 10-13.5 cm., transverse 8-9.5 cm., diagonal 12-14 cm. The brain of the infant is normally rosy-red in color, rather translucent, soft, almost jelly-like, and moist. Tearing of the pial veins or meningeal arteries during delivery may produce fatal meningeal hæmorrhages.
The weights of the internal organs are: brain 380 grms., thymus 7-10 grms., heart 20.6 grms., lungs 58 grms., spleen 11.1 grms., kidneys together 23.6 grms., testicle 0.8 grm., liver 118 grms. The mature placenta weighs about 500 grms., and measures 15-20 cm. ”

“ At the upper end the chain of each side passes up into the cranium and is closely connected with the cranial nerves. In the neck, branches pass to the lungs and the heart. From the ganglia in the chest three nerves form a complicated network of fibers, from which branches pass to the stomach, the liver, the intestines, the kidneys, and other abdominal organs. A similar network of fibers is situated lower down in the pelvis, from which branches are distributed to the pelvic organs. ”

“ The new doctrine he expounded was received in Germany with great enthusiasm by the school of the philosophers of nature. The author conceived the cranium to consist of three vertebræ, and the basal occipital, the sphenoid, and the ethmoid, were regarded as the central parts of these cranial vertebræ. On these alleged bodies of vertebræ, the arches enveloping the central parts of the nervous system were raised, while on the opposite side were attached the inferior pieces, which went to form the vegetative arch destined to embrace the intestinal canal and the large vessels. ”