Osseous System. 163 



popotamus, Rhinoceros, Peccary, Wart-hog, Tapir, Horse, Zebra, &c., 

 and the ruminants which embrace the Camel, Lama, Musk, Deer, Stag, 

 Antelope, Sheep, Goat, Buffalo, Giraffe, domestic Ox, &c. As their 

 fore feet are used for walking exclusively, and constantly support the 

 weight of the animal, the compression strains are thrown upon the scap- 

 ula, which is developed in all, and a tension strain is thrown upon the 

 part usually occupied by the clavicles. The Horse, Pig, Hippopota- 

 mus, and Tapir ( and doubtless others ) possess a remnant of the cora- 

 coid reduced to a mere tubercle. The Hippopotamus also has a short 

 acromion process or prolongation of the spine of the scapula, to which 

 the clavicle would be articulated, if there were one. Related to the un- 

 gulata are the herbivorous sea mammals, the Manatus or Mermaid, and 

 the Dugong or Siren. These are destitute of clavicles like the rest of 

 the ungulates, but their scapula possesses a spine. 



The Cetacea ( Dolphins, Porpoises, Whales, &c. ) sea mammals 

 are also destitute of clavicles, but some of them have straight and flat- 

 tened coracoids. These animals are descended from land mammals, 

 vfhich probably did not possess coracoids, but having again taken on a 

 habit of swimming, they are, doubtless, in process of reacquiring these 

 parts anciently developed in the lower vertebrates by that habit. 



In examinations of this kind it is not always practicable to determine 

 how much of a given characteristic is due to the habit as practiced by 

 the present generation, and how much to a different habit practiced by 

 its remote predecessors. An individual may now have a habit that is 

 in antagonism to the habits of his ancestors, and, therefore, is tending 

 to undo the anatomical development which " they built up. When we 

 find a fish on land, walking across the country on its fins, we will not 

 conclude that the fins have been differentiated into their present shape 

 by walking. On the contrary, we should suppose that such habit in 

 the fish is a new one not indulged in by the "ancestors in whom the fins 

 were developed, and that, if persisted in during a sufficient number of 

 thousands of generations, might be expected to have a modifying effect 

 on the shape and functional value of the fins. Many of such points can 

 be settled by comparative anatomy. We should hardly have been able 

 to discover that our " coracoid process " was a remnant, which for some 

 millions of years has been on its road to extinction, if we had not been 

 able to see a perfect original in our lower vertebrate cousins. We might 

 have supposed, in the absence of such testimony, that our present hab- 

 its were such as to develop such a "process" up from the scapula. 

 But now we know that it is the other way, and that the coracoid has 

 been developed down to become the "process." 



The future of comparative anatomy is destined to make us acquainted 

 with our anatomical history in detail, to point out the relationship and 



