518 ANATOMY OF VERTEBRATES, 



opening, behind which it sends off the pulmonary artery, and 

 returns, at an acute angle, to join the third vascular arch near its 

 termination in the aortic root; or, the pulmonary artery may be 

 said to be formed by a small branch from the third arch, in con- 

 junction with the fourth arch. The branchial arteries are sent off 

 from the aortic trunk, about an inch beyond its origin. 



In the Newt the small anastomosing vessel at the base of each 

 gill, between the ingoing and outcoming trunks, enlarges as the 

 flow of blood is checked by the stunting of the gill in the course 

 of its absorption ; so that, when this is complete, the blood flows 

 from the ' bulbus ' round to the aorta in a continuous unchecked 

 stream, fig. 333, as at its first appearance. 



In the Frog this course of change issues in the following per- 

 sistent disposition of the primitive vascular arches :- — The anterior, 

 originally the fourth, pair, which have their origins brought back 

 so as to seem to rise from the pair preceding, are sometimes called 

 its ' carotid branches : ' they diverge outward, as in their primitive 

 course, have a partial enlargement, and send off the ' lingual,' 

 pharyngeal, and entocarotid arteries. The next pair of vascular 

 arches, answering to the third of the primitive pairs, sends off 

 the laryngeal and brachial ai'teries, also a tributary to the sub- 

 cutaneous cervical, and are continued backward and inward, 

 supplying the oesophagus in this course, to form by their union 

 the aorta, a. The first pair, answering to the second and first 

 of the primitive pairs, send off the second root of the artery 

 which ramifies on the subcutaneous cervical gland, and the 

 pulmonary artery ; the dorsal part of the second primitive arch 

 now appears as the accessory root of the subcutaneous cervical 

 artery given off from the aortic root, as above mentioned. 



The brachial artery sends off an external thoracic, distributed 

 to the muscles of the fore-part of the abdomen, a subscapular 

 branch, a circumflex artery, supplying the muscles of the shoulder, 

 and is then continued to the fore-arm, where it becomes ' radial,' 

 sends off a recurrent branch, and divides near the wrist into a 

 dorso-carpal and palmar branch, which terminates in the digital 

 arteries and the intervening web of capillaries. 



The aortic trunk gives off the gastro-mesenteric artery, dividing 

 into ' coeliac ' and mesenteric branches ; then the suprarenal and 

 renal arteries, the lumbar, and the genital arteries (spermatic or 

 ovarian), and bifurcates to form the common iliacs. From each 

 of these are sent off a vesico-epigastric artery continued from the 

 allantoic bladder forward upon the abdominal walls, the external 

 and internal circumflex arteries, and the femoral, which, on reaching 



