Tii DR, N. H. ALCOCK OlH THE VASCTJL,1R [Feb. 1, 



1 mm. from the oiigin of the vertebral the thj'roid axis, a sleuder 

 vessel running forward, is given off, and from this the subclavian 

 pursues a course almost dii'ectly outward, and arching across the 

 lirst rib is continued into the axillary. 



The two Internal Mammary arteries (figs. 1 and 7) differ 

 somewhat on the two sides. The right internal mammary, rather 

 larger than the left, arises from the subclavian, and turuing round 

 the right preca\al vein runs at first obliquely iuward and back- 

 ward, between the pleura and the chest-wall, and embedded in the 

 substance of the ventral part of the thymus gland. After a little 

 the common mammary vein joins the artery, lying to its iuuer side. 

 Beaching the junction of the presternum with the mesosternum, 

 the artery passes backward, and finally divides opposite the sixth 

 costal cartilage into the musculo-phrenic and superior epigastric 

 arteries, the latter considerably the larger and continuing the 

 direction of the parent trunk. 



The branches of the internal mammary artery are : — 



1. A branch arising 11 mm. from the subclavian, which runs 

 forward and inward (fig. 7) to the suprasternal notch, where it 

 divides into several branches to supply the upper part of the 

 thymus, the trachea, the infrahyoid muscles, and the anterior part of 

 the pleurae, and sends one slender t\\ ig outward along the anterior 

 border of the clavicle. This branch 1 have called prcsternal. 



2. Ventral perforating arteries, which supply the pectoralis 

 major and adjacent muscles. In the first intercostal space one 

 perforating artery appears at the upper part of the space and one 

 at the lo\Aer ; all the subsequent spaces have only one each, appearing 

 at the lower border of the space. In this species all these arteries 

 do not differ much in size, but in many of the Microchiroptera 

 ( V. noctula e. g.) the first and fourth (third space) are much larger 

 than the rest. 



3. Venti'al intercostal bi'anches. Two in each space except the 

 1st," arising separately from the internal mammary, and with a 

 course as in man along the margins of the ribs. The branch at the 

 posterior edge of each space is a \ ery minute vessel. 



I could not discern any branch corresponding to the arteria 

 comes nervi phrenici of human anatomy. 



Ihe Left Internal Mammary Artery has a similar origin to the 

 right. It turns round the left precaval \ein, and passes to a similar 

 position by the side ot the mesosternum, giving off no branches 

 until it reaches this point. Here it first meets with the left 

 internal mammary vein, which lies internal to it, and for the rest 

 of its course resembles exactly the artery of the right side. 



Thoracic Veins. 



Right Precaval. — In the lower part of the neck three venous 

 trunks join — the vertebral, the internal jugular, and the external 

 jugular, the two former nearly equal in size, the latter as 

 large as both taken together (fig. 1). After a course of 

 2'5 mm. the common trunk thus formed joins with the subclavian, 

 at a point hmuediately above the sterno-clavicular articulation, and 



