REPORT ON THE ANATOMY OF THE PETRELS. 31 
absent. It is fairly broad and ribband-shaped, overlapping the semi-membranosus in the 
Oceanitidz at its origin, and inserted into the femur together with the femoro-caudal. 
In the genera Fregetta, Puffinus, and Majaqueus it is decidedly small. 
The semi-tendinosus (t.c., figs. 1-3, s.t.) muscle is always present and strong. It 
arises from the iliac bone round its most posterior angle, and has no connection at all 
with the caudal vertebra. Anteriorly it slightly overlaps the biceps. 
Excepting in the Oceanitide, it has no accessory head, so that all its fibres are 
inserted by a thin, broad tendon, quite distinct from that of the semi-membranosus, on 
to the tibia. In the Oceanitidze, in all the species and genera, there is a strong and 
broad accessory head, arising from the femur, as usual, and joining the main belly of the 
muscle by an oblique tendinous raphe (vide Pl. V. fig. 3, a.s.t.). 
The semi-membranosus (t.c., figs. 1-8, s.m.) is always very large, of broad, flat, 
ribband shape, not so parallel with the semi-tendinosus nor so covered by it, as usual, 
its direction being more oblique than is that of the other muscle, and thus more parallel 
to that of the adductors. It arises from the posterior margin of the ilium, ischium, and 
pubis, from a little above the ischial prominence to within a small distance of the end of 
the pubis. Its insertion is by a thin, broad tendon, anterior to, and separate from, that 
of the semi-tendinosus. 
Of the other muscles in the hind-limb the biceps always passes through a tendinous 
loop on its way to its insertion, as is nearly always the case with birds. 
The obturator externus is never large, and is inserted near the femur head. The 
obturator internus is of peculiar shape, nearly oval, but with a slight indication of 
becoming triangular. ‘The deep flexors of the toes and of the hallux blend, usually about 
half way down the leg, and their tendons may become ossified. Even when a hallux is 
present it receives no tendon at all from these muscles. 
4, OrHER ANATOMICAL FEATURES. 
There are always two carotid arteries situated in the hypapophysial canal. There 
are also two jugular veins, the right of which is frequently the largest. 
The main artery of the leg is always the sciatic one, accompanying as it does the 
sciatic nerve. 
In the genus Pelecanoides, as has already been described by Garrod (cf: antea, p. 10), the 
femoral vein, instead of being, as usual in birds, deep of the femoro-caudal muscle,—from 
the external border of which it then seems, in the ordinary course of dissection for the 
thigh-muscles, to emerge (Pl. V. fig. 2, fv.),—is superficial to it, appearing at the external 
edge of the obturator externus, and then crossing the femoro-caudal superficially as 
represented in Pl. V. fig. 4, fv. 
