ARTERIES OF MAMMALIA. 543 



the fifth pair of ribs, gives off a very short trunk, which divides 

 into the right brachio-carotid and the left carotid ; the aorta then 

 sends off the left brachial artery which has a long course in the 

 chest before it attains and bends over the first left rib. The 

 brachio-carotid has a course of an inch before dividing. The 

 carotids do not divide until they have passed the atlas, and the 

 ectocarotid is larger than the entocarotid : small plexuses are 

 formed in the orbits and temporal fossse. The brachial, after 

 bending over the first rib and traversing the axilla, suddenly 

 sends off and seems to break up into a fasciculus of minute longi- 

 tudinal branches, which surround and conceal the main-trunk. 

 This, however, exists in the middle of the plexus, contracted at 

 first, but gradually resuming its more normal dimension as the 

 brachial artery, and that not by the reception of any of the pre- 

 vious ramuscules. It begins to diminish again at the elbow, and 

 thence gradually contracts until it forms the radial side of the 

 palmar arch and the chief origin of the two digital arteries that 

 go, one to each interspace between the middle and the two lateral 

 fingers : the ulnar side of the palmar arch is formed by a con- 

 tinuation of one of the branches sent off from the axillary, and 

 the rest of that plexus is distributed progressively to the muscles 

 and other parts of the limb, eight or ten of the branches quitting 

 the main trunk at the bend of the elbow to perforate the inter- 

 osseous space or to supply the deep-seated muscles of the fore-arm. 



Thus, the arterial stream is propelled directly by the main 

 trunk to the digits ; the force being broken by the sudden dis- 

 persion of the current in the score of branches sent off from 

 nearly the same part of the circumference of the axillary artery. 



The vertebral artery is sent off at the brim of the thorax on 

 both sides. The phrenic pierces the diaphragm with the aortic 

 trunk, winds round the right of the oesophageal aperture, and 

 soon divides. The gastric artery is as large as the superior 

 mesenteric. The renal artery gives off the spermatic. The 

 abdominal aorta bifurcates opposite the last lumbar vertebras. 

 The left iliac, in my subject, sent off, at its origin, the arteria 

 sacra media and the two epigastric arteries : the former soon re- 

 solves into a plexus. The right iliac also sends a few branches 

 to the sacral plexus; but this is formed chiefly by branches 

 sent off around the origin of the sacromedian trunk. The in- 

 ternal iliac is represented by a plexus coming off by three or 

 four quickly-dividing branches from the common iliac before it 

 passes over the brim of the pelvis : at this part, also, the femoral 

 plexus begins to be given off by one or two branches which sub- 



