MUSEUM OF COMPAKATIVE ZOOLOGY. 47 



In view of the interest attaching to this subject, I have thought it 

 not wholly supei'tiuous to put on record still another example of the 

 persistence of the right root of the a. subvertebralis, — especially since 

 so perfect a root from so old a specimen has not been heretofore men- 

 tioned, and since no figure of this condition at any stage has, to my 

 knowledge, been heretofore published. 



The specimen in question was one which was being used for study in 

 the class in Vertebrate Anatomy by one of my pupils, Mr. H. 0. Marcy, 

 The Alligator was about 2S cm. long. The arteries had been injected 

 from the heart, and a very evident branch, F'igure 1, 1*', was shown, fully 

 mjected, running from the right common carotid, h, to the a. subverte- 

 bralis 1* + P'. Thus the whole carotid system had a very symmetrical 

 aspect. The branch in question (l"')' which must be regarded as the 

 proximal end of the right dorsal carotid, was injected throughout its 

 whole length. It measured 0.7 mm. in diameter, the corresponding 

 measurement of the left root being 1.0 mm. The two trunks passed 

 dorsally, encircling the trachea and oesophagus, and met near the median 

 plane, dorsal to the oesophagus and immediately beneath the vertebral 

 column. 



I add also figures of two cases of persistent ductus Botalli, completing 

 the VI. or pidmonary arch. Some trace of this condition appeared upon 

 most of the individuals examined. In one case shown (Fig. 3), the in- 

 jection filled only tlie dorsal and ventral ends of the ductus, the middle 

 region remaining as a white cord. In the other case (Fig. 2), the pul- 

 monary end only was injected. 



Finally, in a simple diagranniiatic lateral view (Fig. 4), built up on 

 the S3'stem of Rathke's diagrams, as improved by Boas ('87), I have 

 indicated the chief neck-arteries of the Crocodilia. In this diagram, 

 the usually occurring arteries are drawn in heavy lines ; those occurring 

 less regularly or abnormally, in fine lines ; those absent, in dotted lines. 

 I have introduced as the II. arch the anastomosis between P and 2 

 (Fig. 1), thus adopting van Bemmelen's ('88, p. 115) suggestion; but 

 I must repeat his caution, that this is onlj' a rather probable, but by 

 no means demonstrated homology. 



