— ~ 
NECTURUS MACULATUS. 433 
The lmbs when in the normal resting or swimming position are directed backwards, 
and are held in such a way that in the hind limbs the soles face inwards, while in the 
fore limbs the dorsal surface of the manus is ventral, and the palm dorsal. This is apt to 
cause considerable difficulty in orienting the parts, but if the action of the limbs be 
watched in a living animal it will be seen that this position is due, not so much to a 
torsion, as to a swinging of the entire limb at the shoulder. The position assumed by the 
fore limb is the easier to understand, and in this it is evident that the limb when extended 
forward as in walking, rests with the palm down and the dorsal surface of the manus up, 
but that when the entire limb is swung from the shoulder so as to change its direction and 
point backwards, the positions of palm and dorsum are necessarily reversed. In the hind 
limb there is some tendency to counteract this by a torsion of the limb about its own axis 
and thus in a trailing hind foot the sole is turned somewhat inward. 
Humerus.— The humerus, like the other long bones of the limbs, consists of an 
osseous shaft and two cartilaginous epiphyses. The usual cylindrical shape is retained 
only at the middle while the ends are both strongly flattened, and at right angles to 
one another, the proximal end being flattened laterally, and the distal end dorso-ventrally. 
The most prominent part of the proximal epiphysis is the head, which fits into the glenoid 
fossa of the shoulder girdle and forms the characteristic ball-and-socket joint. It is sub- 
spherical in shape, and is slightly affected by the general flattening of the entire region. 
Its ventral face is prolonged into a sharp ridge which is continued by the osseous 
diaphysis and forms one of the most distinctive features of the bone. This is the crista 
ventralis (crista deltoidea of Ecker) and serves for the insertion of most of the ventral 
shoulder muscles. This crest is highest near the junction of cartilage and bone and 
rapidly recedes, so that at the middle of the diaphysis no trace remains. 
The distal end, which is broadened laterally and flattened dorso-ventrally, bears an 
extensive median furrow running around the end and up both surfaces, and dividing it 
into two masses which may be distinguished as the external (lateral) and the internal 
(median) condyles, although they include parts which in higher forms are distinct from 
the condyles themselves. The external condyle is somewhat the larger and is ball-shaped, 
fitting into the socket in the head of the radius. It also serves as a point of origin for the 
extensor muscles of the forearm and hand. Having these two functions, it plainly corre- 
sponds to both the external condyle and the capitulum of higher animals (epicondylus 
medialis and eminentia capitata of the frog; Gaupp). 
The internal condyle is more nearly the exact homologue of the part of that name in 
higher forms as it gives origin to the flexor muscles of forearm and hand, but does not 
participate as directly in the formation of the elbow joint. The groove between the two 
condyles lies in the greater sigmoid notch of the ulna, and the olecranon of the ulna and 
