42 Frederic T. Lewis. 



anomaly to be described. At the outlet of the subclavian vein there 

 are several branches, and among them the anterior jugular vein can 

 be identified. 



The anomaly which led to the examination of the embryos is pic- 

 tured in Fig. 5. If the small vein ventral to the subclavius muscle 

 in Fig. 4 is considered to have enlarged and anastomosed both with 

 the cephalic vein and the subclavian vein, the conditions found in the 

 anomaly will be strikingly reproduced. Both the clavicle and the 

 subclavius muscle will then be surrounded by a venous ring. In the 

 anomaly the "jugulo-cephalic" vein, which is above the clavicle, is as 

 large as the subclavian vein. The "accessory subclavian vein," which 

 is between the clavicle and the subclavius muscle, is somewhat larger. 

 The subclavian vein occupies its normal position between the sub- 

 clavius muscle above, the scalenus anterior behind, and the first rib 

 below. 



Finally it may be noted that the formation of a venous ring around 

 the scalenus anterior muscle, occasionally recorded in the adult, is 

 suggested in the 22.8 mm. embryo. 'Where the subclavian veiin 

 empties into the jugular, these vessels are molded about the muscle, 

 and since a vertebral branch joins the jugular at this point, nearly 

 two-thirds of the circumference of the scalenus anterior are in rela- 

 tion with the veins. The completion of this ring by venous out- 

 growths Avould account for the anomaly. The conclusion may be 

 drawn that although the jugulo-cephalic vein in man is a persistence 

 of an important and normal embryonic vein, the accessory subclavian 

 vein, whether situated behind the scalenus or above the subclavian, 

 is an abnormal vessel. 



Of wider interest is the conclusion that the lingno-facial vein is a 

 morphological constant. In mammals it appears at an early stage, 

 and although it often becomes resolved into a group of branches, it is 

 present in the adult. Some of its transformations in man are showTi 

 in Fig. 6, on the preceding page. It may have large anastomoses 

 with the external jugular vein or the anterior jugular vein or with 

 both, but these can be readily described and understood on the basis 

 of a primary linguo-facial vein. 



