THE SKULL 



of the occipital-parietal contact is shown by the fact that the latter situa- 

 tion obtains in pigs, in which the occipital plane is tilted quite far 

 backivard. And that no stimulus of such sort is absolutely necessary is 

 shown by the fact that broadening of sutural contracts between parietal 

 and squamosal is well developed in at least some of the Kangaroos 

 {Macropus) and very likely some other terrestrial mammals. The in- 

 ference is therefore that such telescoping of the posterior cranial ele- 

 ments as results purely in the extension of one bone over the other so as 

 to broaden the line of contact may be either a character of no conse- 

 quence (as far as we can see) other than possibly a phylogenetic one: 

 may be largely caused by a forward tilting of the occipital, backward 

 pressure frequently applied to the skull, or both. 



Invariably, I believe, it has been stated that the rostral tilting of the 

 occipital plane of the mysticeti, and inferentially of fossorial rodents, 

 is for the purpose of muscular strength, at which point the topic is 

 abandoned without qualification or explanation regarding the quality 

 of strength that is meant. Such strength is of five sorts, or is indicated 

 in five separate ways, which fundamentally affect the conformation of the 

 occipital shield by reason of the fact that the supraoccipital muscles seem 

 utterly incapable of migrating from one bone to another, so that when 

 they shift the supraoccipital must shift with them. In order properly 

 to understand the cetacean conditions in this region of the skull it will 

 be necessary to scrutinize the situation in certain pertinent terrestrial mam- 

 mals, under five separate headings as follows: 



{A) There is the strength exemplified in the occipital conditions 

 of the lion or pig. The former must have powerful neck muscles of 

 a sort to enable the head to be strongly twisted in all directions in order 

 that it may, for instance, break the neck of a zebra. The pig roots in 

 ground that is often hard, can do this all day long, and can lift a truly 

 astonishing weight with its snout. This sort of active muscular strength 

 is accompanied by high and strongly-defined lambdoidal ridging along 

 the supraoccipital border. 



(B) A different situation is encountered in mammals which we 

 know must have great strength of occipital musculamre for the support 

 of a heavy equipment of horns or tusks, but which have no particular 

 need for cephalic activity, embodying strong twisting motions. Although 

 not occurring in its perfected, simplest form, this sort of passive muscular 

 strength is illustrated by the moose and others of the deer tribe with large 

 antlers, large-horned bovines, and old male elephants. The bony indi- 

 cations of this character of muscular strength do not take the form of 



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