H. S. Jennings

“ Lingua (Fig. 95) .—The tongue is a muscular organ covered with mucous membrane; in life it is very mobile. It is an elongated organ, flat above, broadest in the middle, and very slightly narrowed at each end. It extends from the incisor teeth to the isthmus faucium and nearly fills the mouth cavity. The caudal third of the tongue forms the floor of the mouth cavity, so that the tongue has here no ventral surface, but is directly continuous with underlying organs. It is in this region that the extrinsic muscles of the tongue (except the genioglossus) enter it. ”

“ Dorsal Rami (Rami posteriores) .—The dorsal ramus of the first nerve (N. suboccipitalis) supplies the short dorsal muscles which move the head and connect the atlas and skull. In the second nerve the dorsal ramus is much larger, forming N. occipitalis major. It sends small branches to the muscles about its origin, then turns craniad on the surface of the obliquus superior muscle, passes through the biventer cervicis and splenius, joins a small branch from the third nerve, and reaches the dorsal surface of the back of the head. ”

“ The caudal portion arises from the lateral surface of the manubrium along the dorsal half of its cranial end, and from the median raphe for about one centimeter craniad of the manubrium. Its fibres are parallel and tend to diverge into two layers. The cranial portion arises by means of fibres which cover the median line and interdigitate with the fibres of the opposite muscle between the cricoid cartilage and a point a few millimeters craniad of the manubrium. Its caudal border is thus overlaid by the caudal portion. Its fibres converge and join those of the caudal portion. ”

“ The muscle-fibres take origin from the strong craniolateral part of the inner surface of the temporal fascia, from the groove on the temporal bone dorsad of the dorsal root of its zygomatic process, from the whole inner surface of this process and of the zygomatic process of the malar bone, and sometimes also from that part of the frontal bone which lies within the temporal fossa. ”

“ It does not pass directly to the stomach, but passes first ventrad of the small intestine as far as the pelvis. Thence it turns craniad to reach the greater curvature of the stomach. The fold thus formed is called the great omentum. It forms the dorsal and ventral walls of a sac, the omental sac, the cavity of which is called the lesser peritoneal cavity. The descending limb of the fold forms the dorsal wall of the sac, and its ascending limb forms the ventral wall. Each of these walls is double like a mesentery, so that the great omentum consists of four sheets of peritoneum. ”

“ The spinal cord is a nearly straight tube, with a central cavity and thick walls. The brain is likewise tubular, with the cavities enlarged or subdivided in places, with the walls greatly thickened, and with a number of bends and constrictions in the tube. The relation of the structure of the brain to that of the spinal cord is most easily perceived by an examination of the brain of some lower vertebrate, as the frog or shark, and such an examination should be made before proceeding to the study of the more complicated brain of the cat. ”

“ Two others pass one from each side of the bladder to the dorsal body wall at the sides of the rectum. They are the lateral ligaments of the bladder. They form the walls of a partly isolated peritoneal pocket into which the rectum passes; this pocket opens craniad into the peritoneal cavity. The wall of the bladder is composed of an internal epithelium, a layer of plain muscle-fibre bundles which cross one another in various directions, and the external peritoneal layer. ”

“ The Larynx. The larynx is the enlarged upper end of the air-passage which leads from the pharynx to the lungs. It is a box composed of pieces of cartilage connected by ligaments and moved by muscles, and it is lined by mucous membrane. At the root of the tongue about one centimeter caudad of the body of the hyoid bone is the triangular leaf-like epiglottis (Fig. 95, e, page 227) . When food is taken this closes the opening into the larynx, and the food passes over it into the œsophagus. It is so curved that its apex is directed craniad. ”

“ Each testis lies in a diverticulum of the abdominal cavity, which is lined by an extension of the peritoneum. The testis has the same relation to this peritoneal diverticulum that the intestine has to the abdominal cavity; i.e., it does not lie within the cavity of the diverticulum, but is suspended apparently within it by means of a fold of its wall which acts as a mesentery. The peritoneal diverticulum is called the tunica vaginalis propria and consists thus of a parietal layer and a visceral layer. ”

“ The coronary sinus receives blood from coronary veins, which collect it from the walls of the heart.
In the auricular septum ventrad of the opening of the inferior vena cava is seen a faintly marked smooth oval depression, the fossa ovalis. When the auricular septum is examined by transmitted light it is seen to be thinner over the fossa ovalis. There is an opening, foramen ovale, at this point in fœtal life, so that the blood of the inferior vena cava then passes directly from the right auricle to the left auricle. ”

“ They lie deeper than the muscles previously described. The muscle is most strongly developed in the lumbar region (Fig. 70, d) , where it forms a thick interwoven mass in which it is difficult to distinguish separate bundles. The fibres in this region have origin on the accessory or mammillary processes and usually pass over more than one vertebra between origin and insertion; their insertions reach the dorsal ends of the spinous processes, so that part of the muscle lies immediately beneath the lumbar fascia. In other regions the multifidus is covered by other muscles. ”