The _external jugular_, Fig. 60, ej, after separating from the subclavian, may be traced cephalad, close beneath the skin, to the base of the skull, where it is connected with the internal jugular by short branches, as has already been noted. It receives several small branches from the skin and muscles of the neck and shoulder regions. At the region of its anastomosis with the internal jugular it receives a large branch, the _muscular_, ms, from the massive muscle at the angle of the jaw and from the skin of that region. A short distance cephalad to the muscular the external jugular receives, on its mesial side, two or three branches from the trachea, larynx, and œsophagus, tr. Anterior to these vessels the external jugular is formed by the union of two chief veins, the _lingual_, l, from the ventro-lateral surface of the tongue, and the _inferior dental_, id, from the mesial surface of the lower jaw. The connection of the _superior dental_ (extending along the bases of the maxillary teeth) with the jugular could not be determined with certainty, hence that vessel is not shown in the figure. The same is true of the small veins in the region of the cranium. THE ARTERIAL SYSTEM _The Abdominal Aorta and its Branches._ The right and left aortic arches, Fig. 61, Aod, Aos, arising from the heart in the manner already described, form a rather long loop and approach each other in the middorsal line. Here they are united by a short, wide connective in such a way that the left arch seems continued into the cœliac artery and the right into the dorsal aorta proper. Each arch, anterior to the connective, gives off two fairly large branches, oe, to the posterior region of the œsophagus. The _cœliac_ artery, Fig. 61, c, is the largest branch of the abdominal aortic system. After giving off a couple of small branches, oe, to the posterior region of the œsophagus, it gives off a large _spleno-intestinal_ artery, si, to the spleen and small intestine. The cœliac then breaks up into three arteries of about the same size: the _gastro-hepatico-intestinal_, ghi, carrying blood to the stomach, liver, and small intestine; the _pancreo-intestinal_, pi, leading to the pancreas and small intestine; and the _gastric_, ga, to the greater part of the stomach. From the _dorsal aorta_ proper, da, which, as has been said, seems to be the direct continuation of the right aortic arch, several arteries are given off; these will be described as they occur in an antero-posterior direction. At about the point of union of the two aortic arches arises the most anterior of seven or eight pairs of _lumbar_ arteries, lu 1-7; this first lumbar artery is continued cephalad for some distance as a longitudinal trunk that gives off several lateral branches to the walls of the thoracic region. The other six or seven lumbars are distributed to the dorsal body wall, and arise, at more or less regular intervals, as far caudad as the sacrum, or even back of that point. [Illustration: