152 THE VOYAGE OF H.M.S. CHALLENGER. 



through a foramen between the middle and outer metatarsal bones to the back of the leg, 

 while the other continues its course along the front of the metatarsus to the base of the 

 digits, where it divides into two branches for the supply of the contiguous sides of the middle 

 and outer toes. 



Comparative Eemarks. 



Having now completed the description of the arterial system of the Penguins, it may 

 be well in a few words to compare it with that of other birds. 



The arrangement of the carotid arteries of bii-ds has formed the subject of special essays 

 by Bauer/ Meckel," Nitzsch,' and Barkow,* all of whom have directed attention to a num- 

 ber of variations in respect of the arrangement and distribution of these trunks in different 

 species. Among these various observations, Meckel ^ directs attention to the fact that in 

 the genus AjJtenodytes (species not mentioned) the two common carotids are of equal size, 

 and that they are symmetrically arranged, and come off from the innominate arteries of 

 opposite sides. Since that observation, I cannot ascertain that anything definite has been 

 put on record with regard to the arterial system of the Penguins, until the late 

 Professor Garrod,^ in his paper " On the carotid arteries of birds," extended the 

 observations of Meckel, and showed that in Sj^heniscus demersus, Spheniscus humholdti, 

 and Aptenodytes pennantii, the common carotid arteries are of equal size. These 

 observations I have now been able to confirm, and to show that they apply to every 

 species of Penguin which I have had an opportunity of examining. 



If now we look to the arrangement of the other arteries in the Spheniscidse, we find 

 that every member of the group is farther characterised by the possession of two arterial 

 arrangements, which, taken together, appear to be characteristic of the group as a whole. 

 I refer to the distribution of the arteries of the anterior and posterior extremities. In 

 respect of the latter, as already noticed, the principal artery of the limb is not, as is usually 

 the case in birds, the sciatic, but the crural trunk. Indeed, so far as I could ascertain after 

 careful dissection of every species at my disposal, the sciatic artery is absent, excej)t in 

 Spheniscus mendlculas, in which I found a very minute twig derived from the abdominal 

 aorta, accompanying the sciatic nerve. With this single exception, the crural artery 

 entirely replaces the sciatic, and supplies those branches which in the majority of birds 

 are supplied partly by the femoral, but chiefly by the sciatic artery. As before observed, 

 Mr. Forbes informs me that he has discovered a similar arrangement in certain other birds, 

 but in none " that can at all be considered as allied to the PeuQ-uins." ^ 



o 



• Disquis. circa nonnuUarum Avium systema arteriosum, Berolini, 1825. 



• Beitrag ziir Gesohichte des Gefasssystem der Vogel, Meckel's Archiv, 1826, pp. 19 and 157. 

 ' Observationes de Avium arteria carotide commune, Hallre, 1829. 



■• Anatomisch-physiologisehe Untersuchungen iiber das Schlagadersystem der Vogel, Meckel's Archiv, 1829, p. 305. 

 ^ Anatomie Comparee, vol. ix. p. 363. 

 « Proc. Zool. Soc, 1873, p. 457. 

 ' Letter to the author. 



