PLATANISTA. 461 



wards ; tlie former after its origin gives off a considerable branch from its right 

 side to the thyroid gland, but after this it runs forwards imbranched for about four 

 inches. A mass of vessels then arise, first a bundle from its left and then another 

 from its right side, the two being in close relationship to each other. In these 

 combined tufts I have counted as many as fifteen branchlets, each of which, imme- 

 diately after its origin, broke up into numerous smaller vessels producing an intricate 

 rete mirabile. About one inch beyond this, the carotid passes below the posterior 

 angle of the root of the zygoma, and at this point again gives off another tuft of 

 vessels likewise forming a rete mirabile. It then dips below the glenoid process 

 of the squamous, and at the anterior extremity of the tympanic is again resolved 

 into yet another and a similar bundle of vessels. Up to this point, in the 

 whole course of the carotid, no prominent branch has sprung, and the cahbre 

 of the artery has been but little diminished, nor is there much reduction here 

 where it terminates in this rete mhabile, among which, however, there are some 

 twigs larger and longer than the others ; but these I have not succeeded in 

 tracing to any distance. It is evident that no large branch enters the interior 

 of the skull, in which probably all the vessels assume the character of a rete 

 mirabile. 



The right subclavian divides at once into two branches, the internal mammary, 

 and the continuation of the subclavian itself, the latter very much smaller than 

 the former. From the anterior surface of the subclavian division a small artery 

 passes inwards below the common carotid coursing forwards along the side of the 

 trachea. The subclavian is continued outwards for a short distance and gives off 

 a branch, the transversalis colli, and then breaks up into a plexus of small vessels 

 constituting a rete mirabile, a continuation of which invests the brachial nerve, no 

 distinct axillary artery existing, and the brachial being only represented by the fore- 

 going plexus. The internal mammary is very large, but one inch from its origin 

 it o-ives off the posterior thoracic artery which rapidly describes a sigmoid flexure 

 and then passes forwards, itself also ultimately breaking up into a rete mirabile. 

 The internal mammary does not divide into a plexus but it becomes small and can 

 be traced a long way backwards. A twig springs from it and runs along the margin 

 of the sternum internally. 



The left common carotid has its origin from the arch of the aorta, about a half 

 inch to the left of the brachiocephalic, and courses forwards for about five inches 

 unbranched ; after this point, it occasionally gives off branches to the thyroid, pre- 

 servino" in the rest of its distribution the same characters and divisions as in the right 

 common carotid. The left subclavian arises close to the side of the left common 

 carotid, separated from it by about 0-30 inch, and passes on undivided for almost 

 an inch when it breaks up into two, a small artery from the point of division pro- 

 ceeding to the thyroid. Of the two branches the posterior is the internal mammary, 

 but where it leads backwards, a few twigs arise to form a plexus. Where the 

 external mammary originates, a small artery runs backwards to the pericardium. 

 The subclavian branch, after a course of an inch and quarter, sends forwards an 



