REPOET ON THE SPHENISCID^. 235 



remarkable attitude of the Penguin when on land ; by the presence and arrangement of 

 the transverse cloacal muscle ; by the great strength of the muscles which act at the 

 shoulder joint, that is, upon the wing as a whole ; by the peculiar disposition of the 

 brachialis internus muscle ; and by the almost complete atrophy of the muscles which act 

 upon the forearm and hand, the last-mentioned peculiarities being associated with the alteia- 

 tion in function of the wing, and its conversion from an instrument of aerial to one of 

 aquatic locomotion. In respect of the muscles of the leg, the Penguins do not diifer 

 essentially from other Palmipedes. 



Passing to the peculiarities of the arterial system of the Spheniscidse, we find that 

 these are no less characteristic of the group than are those of the bony and muscular 

 systems. They consist in (o) the presence of two common carotid arteries of equal size, 

 symmetrically disposed on either side of the middle line ; (h), the peculiar mode of distribu- 

 tion of the subclavian artery, which breaks up into an axillary and brachial rete mirabile 

 from which branches are derived for the supply of the forearm and hand ; (c) in the 

 absence of the sciatic artery as a direct branch of the abdominal aorta, and its substitu- 

 tion by a branch of the crural artery. 



The venous system of the Penguins is characterised by the presence of two jugular 

 veins of equal size, placed symmetrically on either side of the neck ; by the junction of 

 the sciatic with the crural vein, instead of with the inferior vena cava ; and by the 

 presence of a single vena portse, which only subdivides immediately before it enters the 

 liver. 



The digestive organs of the Spheniscidee present fewer characteristic features than 

 do the other systems akeady referred to. The large size of the buccal papiUEe is 

 perhaps more characteristic of the group than is any other portion of their digestive 

 system. The proventricular gland varies in form in different genera, and even in 

 different species of the same genus. As a rule, it is either crescentic in form or pre- 

 sents a completely zonular character. The caeca are small and adnate. The bursa fabricii 

 is usually of exceptionally large size, but both its size and structure vary in accord- 

 ance with conditions concerning the exact nature of which we are at present ignorant. 



The respiratory organs of the Spheniscidee closely resemble those of other bu-ds in 

 their general ari'angement. In one important particular, however, they differ from all 

 with the exception of those of the Procellariidse. The presence of a tracheal septum, 

 which more or less completely divides the air tube into two lateral chambers, is 

 met with only in the SpheniseidiB and in th^ ProceUariidse. This septum is usually 

 but not constantly present in the Spheniscidae. I found it in all the forms which I 

 examined, with the exceptions of EuQlfptes chrysocome . from Tristan d'Acunha, .and 

 Spheniscus minor. The occasional absence of a tracheal septum, therefore, shows that 

 this septum, per se, cannot be considered as a thoroughly and constantly reliable 

 anatomical character of the group of Spheniscidsej any more than of the ProceUariidae. 





