1889.] NATURAL SCIENCES OP PHILADELPHIA. 15 



Flower, W. H. An Introduction to the Osteology of the 

 Mammalia, 1885. Article, "Mammalia" Encyc. Brit. 

 9th Edition, 1883. 

 Forbes, W. A. Coll. Scientific Memoirs. 

 Garrod, A. H. Coll. Scientific Memoirs. 



Huxley, T. H. Elements of Comparative Anatomy. London. 

 1864. A Manual of the Anatomy of Vertebrated Animals, 

 London, 1871. 

 Owen, Sir Richard. Comparative Anatomy and Physiology 



of Vertebrates. 

 Parker, W. K. The Morphology of the Skull. 1887. 



On the Structure and Development of the Skull in the 

 Mammalia. Phil. Trans, of the Royal Soc. 1885. 

 Parker, W. N. "NYiedersheim's Comparative Anatomy of Ver- 

 tebrates. 1886. 

 Parker, T. J. Zootomy. London, 1884. 



Besides numerous special memoirs of other authors and laborers 

 in similar fields. 



A general survey of the Skull and of the investing bones. 

 Professor Parker, I think, would say that the embryo before me 

 was in the " fourth stage," inasmuch as endostosis has at many points 

 invaded the cartilaginous parts, while ossification is more than ap- 

 parent in such investing bones of the primordial skull as the inter- 

 parietal and the supraoccipital, which latter is as yet in two distinct 

 lateral moieties. 



We might describe the form of the skull of this embryo as being 

 subconoid, the apex being represented by the snout, and the hemi- 

 spherical base by the region of the cranial vault and infraoccipital 

 parts. 



Judging from the skull of an adult of another species, Neotoma 

 cinerea, this form materially changes by the time the animal arrives 

 at maturity, for then the skull is quite flat for its entire superior 

 aspect, and from incisor teeth to occipital condyles. Most of the 

 structures of the basis cranii are to be found in a plane parallel to 

 this superior surface. Then, too, frontal, parietal, and interparietal 

 bones do not quite fulfil in the skull of the adult what they promise 

 in the embryo ; by this I mean that as growth proceeds the mesial por- 

 tions gain area over the first and last mentioned elements, and come 

 to be the chief agents in forming the cranial roof. 



