1 644 



HUMAN ANATOMY. 



fibres has been demonstrated from which terminal fibrillse are distributed to the mus- 

 cular tissue and vessels, as well as beneath the epithelium. 



Fig. 1398. 



Pylorus 



■Pyiorus 



THE DUODENUM. 



The duodenum at an early stage is a loop with a forward convexity passing from 

 the pylorus back to the spine. It enlarges into nearly a circle and turns onto its 

 right side, its termination remaining attached below the coeliac axis to the top of the 

 second lumbar vertebra. The part immediately following the stomach remains free, 

 but a little farther back it is suspended from the liver by the diigdeno-hepatic Iiga??ie7it, 



which is the free border of the lesser 

 omentum, containing the portal vein, 

 the hepatic artery, and the bile-duct 

 with the connective tissue about them. 

 This structure is strong enough to de- 

 serve to be called a ligament. The 

 duodenum is therefore nearly a ring sus- 

 pended at two points, one near the 

 beginning and the other (to be de- 

 scribed later) at the end. In the adult 

 the shape is more or less a modification 

 of this imperfect ring. When relaxed 

 and empty it often nearly retains this 

 shape. When distended by inflation 

 or injection it usually shows four parts. The _/?r^/, some 5 cm. (2 in.) long, runs 

 backward from the pylorus, slightly upward and to the right. The beginning of 

 this portion is movable ; later the part is fixed by the structures just mentioned. 

 The other divisions of the duodenum are disposed so as to form a U. The second 

 part descends along the right of the spine to the fourth lumbar \-ertebra. The third 

 runs forward and to the left, with a slight rise. The fourth ascends on the spine to 

 the upper part of the second lumbar vertebra, where, after a sharp bend, — the 

 duodeno-jejunal Jiexure, — it becomes the jejunum. 



Casts of duodenum, showing U- and V-forms. 



The next most common form is the V-shaped, of which there are two varieties. In the 

 more usual one the second part descends, as in the preceding form, and the third and fourth 

 are represented by one which ascends obHquely to the termination. The less frequent variety 

 has the second part inclining forward and to the left as it descends, so that the V is more sym- 

 metrical. A modification of the U-form, which we have called the C-shaped. is characterized by 

 a very short second part, so that the first and third parts are almost in contact. From seventy 

 observations^ on adults (including one girl of fourteen), mostly by means of casts, we find the 

 following forms : 



Male. Female. Sex not noted. 



U-shaped 10 3 9 



V-shaped 9 9 3 



Ring-shaped 2 2 



Indeterminate 7 3 i 



C-shaped 5 



Not to be classified 5 .  2 



38 17 15 



By "indeterminate" is understood those that might be placed in any two of the U, V, or C 

 tvpes, according to the classifier. Those marked "not to be classified" are absolutely irregular. 

 The V-shape is particularly common in women and the irregular forms in men. It should be 

 noted that a v«ry large part of the duodenum lies in an essentially antero-posterior plane,— 

 namely, the first, second, and a considerable portion of the third part, the organ being moulded 

 on the spinal column. The length of the whole duodenum and of its parts is so variable that a 

 statement can be only general. The first part is, according to Testut, 5 cm. , the second S cm. , the 

 third 6 cm., and the fourth 7 cm., the total length of the duodenum being 26 cm., or about 

 10 in. The circumference varies greatly in different bodies. The fourth part is the smallest. 

 The second increases in size as it descends, and the largest point is in either the second or third. 

 The two largest circumferences that we have measured were in the second part. We are sat- 

 isfied that the size of some immense duodena is in no way due to artificial distention ; to what 

 extent it is pathological is uncertain. 



' Journal of Anatomy and Physiology, vol. xxxi., 1S97. 



