HIGH SCHOOL ZOOLOGY. 85 



nature of its component parts are very different. Only one 

 bone, the humerus, effects the attachment and forms the skeleton 

 of the upper arm ; two, the radius and ulna, are in the fore arm, 

 carpal or wrist bones intervene between these and the skeleton 

 of the finirers, which consists in each of a metacarpal bone 

 and three phalanges. How are we to compare these parts with 

 lliose in the catfish 1 It is only possible to do so by studying 

 fishes more primitive in this respect, but investigation appears 

 to show that the humerus is comparable to the metapterygial 

 basal in the catfish, and the other bones to rays in connection 

 therewith. Still greater diffei-ence is to be found in the 

 pelvic arch, for what is called so in the catfish is nothing more 

 than the united basals of the fin, whereas in the Menobranch 

 we have a partly cartilaginous and pai'tly osseous pelvic 

 girdle, with the three constituent regions which we shall find in 

 all the higher foi'ms. Of these the uppermost (ilium) enters into 

 intimate union on each side with the transverse processes of 

 one of the vertebrae. A similar arrangement exists in all 

 Vertebrates except fishes, and the vertebra (or vertebrae) in 

 question, by which this additional stability of the i)osterior 

 extremity is secured, is called sacral. Corresponding to the glen- 

 oid cavity for the attachment of the humerus is the acetabulum 

 for the hip joint. The structure of the skeleton of the hind 

 limb is very similar to that of the fore, and the corresponding 

 parts to those enumerated in the last paragraph are, 1. femur, 

 2. tibia and fibula, 3. tarsal bones, 4. the metatarsals and 

 phalanges. 



6. As the greatest difference in the bony framework is in 

 the limbs, so also the greatest difference in the muscles is to be 

 met with there, but the limbs are of course more differ- 

 entiated in the higher Amphibia, where they have to perform 

 more complicated duties in connection with support and 

 locomotion. 



