Sidney H. Reynolds

“ As regards the endoskeleton, the vertebral centra have terminal epiphyses except in the Ornithodelphia and some Sirenia. In the skull the cranial region is greatly developed as compared with that in lower vertebrates, and whereas in many reptiles the true cranium is largely concealed by a false roof, in mammals the only relic of this secondary roof is found in the zygomatic arch, and postorbital bar. In the adult all the bones except the mandible, hyoid, and auditory ossicles are firmly united together. ”

“ There is never any great development either of the paroccipital process of the exoccipital, or of the postglenoid process of the squamosal. The periotic and tympanic are always fused together; in Cebidae they form a small bulla, but a bulla is not developed in any Old World forms. The periotic is large, especially the mastoid portion, which forms a distinct portion of the skull wall between the squamosal and exoccipital. In Man and still more in Old World monkeys, the external auditory meatus is drawn out into a definite tube, whose lower wall is formed by the tympanic ”

“ In the embryo all the bones contain marrow, but as growth proceeds this becomes replaced by air to a variable extent in different forms. In all birds some part of the skeleton is pneumatic. Many small birds and Apteryx and Penguins among larger ones have air only in the skull; in Pigeons air is present in all the bones except the caudal vertebrae, the leg bones, and those of the antibrachium and manus; in Hornbills every bone contains air. ”

“ The opening of the fenestra ovalis is in the fresh skull occupied by the expanded end of the auditory ossicle, the columella, whose outer end articulates by a concave facet with a trifid extra-columellar cartilage which reaches the tympanic membrane. The lower process of this extra-columella passes into a cartilaginous rod which lies in a canal in the quadrate and is during life continuous with Meckel's cartilage within the articular bone of the mandible. ”

“ The thoraco-lumbar vertebrae are always nineteen. The symphysis of the ischia and pubes is very elongated, and the femur has no third trochanter. The limbs never have more than four digits, and are symmetrical about a line drawn between the third and fourth digits; the digits, on the other hand, are never symmetrical in themselves. The astragalus has pulley-like surfaces both proximally and distally, and articulates with the navicular and cuboid by two nearly equal facets. The calcaneum articulates with the lower end of the fibula when that bone is fully developed. ”

“ The sternum is rhomboidal, and may either be cartilaginous [191] or formed of cartilage bone, but never of membrane bone; it differs from that of birds also in the fact that it does not ossify from two or more centres. An interclavicle is generally present. There are always more than three digits in the manus, and never less than three in the pes. In all living reptiles the ilia are prolonged further behind the acetabula than in front of them, and the bones of the pelvis remain as a rule, distinct from one another throughout life. ”

“ The cervical and trunk vertebrae are generally thought to be flat, certainly their articulating surfaces are not saddle-shaped. There is no long compound sacrum as in modern birds. The tail is longer than the whole body, the caudal vertebrae are twenty in number, they gradually taper as traced away from the trunk, and each bears a pair of feathers. The posterior caudal vertebrae are not united together to form a pygostyle. The upper jaw bears thirteen pairs of conical teeth, planted in distinct sockets in the maxillae and premaxillae, but the mandible has only three pairs. ”

“ The cranium of most vertebrates includes a very large number of bones whose arrangement varies much, but one can distinguish a definite basicranial axis formed of the basi-occipital, basisphenoid, and presphenoid bones, which is a continuation forwards of the axis of the vertebral column. From the basicranial axis a wide arch arises, composed of a number of bones, which form the sides and roof of the brain-case These bones are arranged in such a manner that if both cartilage and membrane bones are included they can be divided into three rings or segments. ”

“ The lumbar vertebrae are often very loosely articulated together and the zygapophyses sometimes as in the Dolphins are placed high up on the neural spines. The centra are large, short in the anterior region but becoming longer behind. The epiphyses are prominent, and so are the neural spines and to a less extent the metapophyses. The transverse processes are well developed, anteriorly they arise high up on the neural arch, but when the vertebral column is followed back they come gradually to be placed lower down, till in the lumbar region they project from the middle of the centra. ”

“ All Primates have the power of pronation and supination of the fore-arm, by the rotation of the distal end of the radius round that of the ulna.
In Man and the Anthropoid Apes the humerus is long and straight, and has a globular head; neither of the tuberosities, nor the deltoid nor supinator ridges are much developed. The olecranon fossa is deep and there is no ent-epicondylar foramen. The radius is curved and has a narrow proximal, and expanded distal end, the ulna is straighter than the radius and has the distal end much smaller than the proximal; the olecranon is not much developed. ”

“ Each half is firmly united to its fellow in a ventral symphysis behind, and is in front expanded and united to the sacrum. Each half or innominate bone is seen in the young animal to consist of four distinct parts, the ilium or dorsal element, the pubis or anterior ventral element, the ischium or posterior ventral element, and a small fourth part, the acetabular or cotyloid bone, wedged in between the three others. These parts, though all distinct in the young animal, are in the adult so completely fused that their respective boundaries cannot be distinguished. ”

“ There are no lumbar vertebrae. The skull is extremely solid, and frequently has a very complete false roof. Teeth have been detected in embryos of Trionyx but with this exception the jaws are toothless, and are encased in horny beaks. The quadrate is firmly fixed. The facial part of the skull is very short, and the alisphenoidal and orbitosphenoidal regions are unossified. In living forms there are no separate nasal bones, while large prefrontals and postfrontals are developed. There is a comparatively complete bony palate chiefly formed of the palatines and pterygoids. ”

“ Neural and haemal arches are however always developed; they sometimes remain separate, sometimes fuse with the centra. Ribs are often wanting and when present are often not separated off from the vertebrae. The cranium is a simple cartilaginous box whose most prominent parts are the capsules which enclose the sense organs. The skull is sometimes immovably fixed to the vertebral column, sometimes articulates with it by means of two condyles. There is no operculum and no representative of the maxilla or premaxillae. The teeth are very variable. Large pectoral and pelvic fins always occur. ”

“ The carpus has the scaphoid and lunar distinct, and generally also the centrale; sometimes however, as in Man, the Gorilla, Chimpanzee, and some Lemurs, the centrale has apparently fused with the scaphoid. There are almost always five well-developed digits, but in the genera Colobus and Ateles the pollex is vestigial.
The magnum in man is the largest bone of the carpus. The pisiform also is well developed, but there is no radial sesamoid. In Man, the Gorilla, Chimpanzee, and Orang, the carpus articulates only with the radius, in most Primates it articulates also with the ulna. ”

“ The hard parts of a tooth commonly enclose a central pulp-cavity into which projects the pulp, a papilla of the dermis including blood-vessels and nerves. As long as growth continues the outer layers of this pulp become successively calcified and added to the substance of the dentine. In young growing teeth the pulp-cavity remains widely open, but in mammals the general rule is that as a tooth gets older and the crown becomes fully formed, the remainder of the pulp becomes converted into one or more tapering roots which are imbedded in the alveolar cavities of the jaws. ”

“ In the two living genera the dentition is monophyodont, but in Halitherium the anterior grinding teeth are preceded by milk teeth. The tongue and anterior part of the palate and lower jaw are covered with roughened horny plates. The skull is noticeable for the size and backward position of the anterior nares, also for the absence or small size of the nasal bones. There is no union of certain of the vertebrae to form a sacrum, and in living forms the centra are not terminated by well-formed epiphyses [120] .
The cervical vertebrae are much compressed, but they are never ankylosed together. ”

“ The next seven thoracic vertebrae are all very similar, each has a long cylindrical centrum, expanded at the ends, and firmly united to the preceding and succeeding vertebrae. The neural arches are flattened and expanded dorsally, and are united to one another and to the overlying neural plates; each arises only from the anterior half of its respective centrum, and overlaps the centrum of the vertebra in front of it. Between the base of the neural arch and its successor is a small foramen for the exit of the spinal nerve. There are no transverse processes or zygapophyses. ”

“ The skin is in most forms at any rate unprovided with dermal scutes. The vertebrae may be with or without zygosphenes and zygantra. The skull resembles that of lizards, having an interparietal foramen, and a cranial cavity open in front. The squamosal takes part in the formation of the cranial wall, and the quadrate articulates with the squamosal, not as in Lacertilia with the exoccipital. There are large supratemporal fossae, bounded below by supratemporal arcades. The teeth are large and acrodont, and occur on the pterygoids as well as on the jaws. ”

“ The membrane bones are the angulo-splenial and the dentary. The angulo-splenial is a strong flat bone which forms the inner and lower part of the mandible for the greater part of its length. Its dorsal surface is produced into a slight coronoid process. The dentary (fig. 26, A, 15) is a flat plate which covers the outer surface of the anterior half of the mandible, as far forwards as the mento-meckelian. The lower jaw is devoid of teeth. The part of Meckel's cartilage which in most vertebrates ossifies, forming the articular bone, remains unossified in the Frog. ”

“ The centrum of each vertebra encloses an isolated vestige of the notochord. The neural arch forms the roof and sides of the neural canal, which is very spacious in the anterior vertebrae, but becomes more depressed in the posterior ones. The arch bears the neural spine, a low median ridge of variable character, and is drawn out in front and behind, forming the two pairs of articulating surfaces or zygapophyses by means of which the vertebrae are attached together. ”