270 CIRCULATORY SYSTEM. 



pancreas by the union of the superior mesenteric with the sple- 

 nic vein, extends from this point to the transverse fissure of the 

 liver, and is about four inches in length. It ascends obliquely 

 from left to right, behind the second curvature of the duodenum, 

 being bounded on the right side by the biliary ducts, and on 

 the left by the hepatic artery, where it is surrounded by a 

 great many nervous filaments and lymphatic vessels, with all 

 of which it is united by a common envelope of cellular sub- 

 stance, and of peritoneum* called the capsule of Glisson. 

 Having reached the transverse fissure of the liver, it divides 

 into two branches, which are each at a right angle to it, but in 

 line with one another : they constitute the Sinus Portarum, of 

 which the right branch being spent upon the great lobe, and 

 the left upon the small lobe of the liver, are ramified almost to 

 infinity through the structure of the latter. The terminating 

 branches of the vena portarum empty into the vena3 hepaticae. 



Several cases are recorded in the annals of anatomy in which 

 the vena portarum, instead of going into the liver, discharged 

 immediately into the ascending cava.* In such instances the 

 hepatic artery is much larger than usual. According to J. F. 

 Meckel, notwithstanding they are anomalies, yet, as in most 

 other cases of deviation from the general type of the human fa- 

 mily, a striking analogy may be found between them and what 

 occurs in some of the lower orders of animals. Here the ana- 

 logy exists with the invertebrated animals. 



CHAPTER IV. 



OF THE PECULIARITIES IN THE CIRCULATORY SYSTEM OF THE 



FCETUS. 



OWING to the want of respiration in the foetus, its circulation 

 is conducted in a manner very different from that of the adult. 

 Moreover, its parasitical life requires an alliance, through the 



* Lieutaud, Hist. Anat. Med. Huber, Obs. Anat. p. 34. Abernethy, Ph. Tr. 

 1793, part i. Lawrence, Mcd. Ch. Trans, vol. v. 



