IN THE LIMBS OF MAMMALIA. 55 



which are right and left repetitions of each other ; and this is often more conspicuous in 

 the Vertebrates, and especially in the Articulates with their sharply defined outlines, than 

 in the almost amorphous forms of the Mollusca ; but here again we must go beneath the 

 surface, and then we find that in the Mollusks not only are the organs arranged upon the 

 two sides of the body, but the " weight of organization," as Professor Agassiz expresses it, 

 is thrown upon the sides, which even in common usage we recognize to have superior 

 value over the front and hind ends, or the upper and lower edges; we examine and figure 

 only the sides, and, except with the Cephalopoda, their natural position is such as to exhibit 

 prominently one of the sides. This distinction between the bilalerality common to all above 

 Radiates, and the laterality proper to the Mollusks, is well set forth by Mr. N. S. Shaler, 

 in the Proceedings of the Boston Society of Natural History, December 4th, 1861. 



With the type of Articulata, it is not the right and left sides that we chiefly regard in 

 either a popular or a scientific examination, but the upper and lower regions, which are, as 

 it were, set off against each other. We no more think of placing or viewing an insect on 

 its side than a bivalve on its upper or lower edge, which correspond to the tergal and 

 ventral regions of the Articulate. This seems to confirm the idea that the single ring 

 representing the articulate unit is composed of an equal number of segments above and 

 below a horizontally bisecting plane, and that the legs and wings when they exist are 

 tergal and ventral repetitions of each other. But the internal anatomy is less satisfactory, 

 at least as now understood, and I leave it to others, more familiar with its details, to 

 determine whether this type, whose sharply defined outlines so clearly illustrate the law, 

 has at the same time the most unsatisfactory internal arrangement ; it is certain that in 

 our present state of knowledge the laterality of the Mollusks is more apparent than either 

 the tergality of the Articulates or the cephality of the Vertebrates. 



This latter term, cephality, applied by Professor Agassiz to the highest type, indicates the 

 extreme preponderance in function of one end of the body ; which, at first on the same level 

 with the other end, is gradually raised, till it attains the greatest possible elevation in the 

 erect position of man. Professor Dana's term, " cephalization," is indicative of this gradual 

 ennobling of one end of the vertebrate body, and, in man, of the devotion of the arms and 

 hands to its requirements, a physiological return to an allegiance they always owed the 

 head, to which, in fishes, they are actually attached. 



In this connection it may be added, that, besides the overwhelming evidence adduced by 

 Professor Owen in support of the view now generally received, that the scapular arch is really 

 the modified pair of ribs of the posterior or occipital cranial vertebra?, there are other facts 

 which indicate that in the early stages of even the higher Vertebrates, the shoulders and 

 head are much nearer together than in their adult condition. 



1st. The singular course of the inferior laryngeal nerve, whence comes its name of the 

 recurrent, is inexplicable on any other than strictly morphological grounds ; for, instead of 

 proceeding by the shortest and most direct route to the larynx from its origin on the pneu- 

 mogastric, it always forms a loop around the subclavian artery on the right side and the 

 arch of the aorta on the left, even in the giraffe, where its length is several times as many 

 feet as it would be inches on the ground of teleology alone. An account of a case of mal- 

 formation, which first drew attention to this peculiarity, was published in the " Edinburgh 

 Medical and Surgical Journal," for 1823, and the same Journal for the month of April, 182G, 

 contains an account of a similar case, with an explanation of this apparent waste of nervous 

 matter. Both of these accounts are quoted on page 379 of "Power's Surgical Anatomy of 

 the Arteries." 



2d. Professor Vrolik, in his work on Monstrosities, "Tabula? ad illustrandam Embryogene- 



