658 SUMMARY OF CURRENT RESEARCHES RELATING TO 



7. Elongation of digits ; hyperphalangy ; hyperdactyly ; formation 

 of smaller skeletal parts. 



8. Concentration of all parts except digits. 



9. Cartilaginous progression in joints ; loss of movable articulations 

 in the limb ; loss of tuberosities for muscle attachment. 



Squamosal Bone in Tetrapodous Vertebrata.* — F. W. Thyng has 

 investigated the homologies of the squamosal. The development of the 

 mammalian squamosal shows it to be a membrane bone which overlies 

 the otic capsule, and is at first intimately connected with the incus 

 (quadrate) by a dense and fibrous stroma. It is concluded that close 

 association with the quadrate (incus) and otic capsule is the primitive 

 relation of the squamosal, and therefore the most important criterion in 

 ascertaining its homology in non-mammalian Vertebrates. Juxtaposition 

 with the parietal is a secondary relation. In Stegocephala, which prob- 

 ably directly or indirectly gave origin to the Mammalia, there exists not 

 only the bone which corresponds with the squamosal as above defined, but 

 a second bone also overlying the otic capsule between this squamosal and 

 the parietal — that is, in the interval which, in the embryonic mammalian 

 skull, is unoccupied by bone. Hence it seems reasonable to conclude that, 

 in the phylogenetic development of the Mammalia, this bone, which may 

 properly be called the supra-temporal, has been lost, and its place has 

 been bridged secondarily by the upward development of the squamosal. 

 No bone has been found in the temporal region of the Cascilian skull 

 homologous with the mammalian squamosal. The bone, so-called, is 

 probably a post-frontal. There is a true squamosal in the Urodelan 

 skull ; it is the bone termed by Gaupp " paraquadrate." In the skulls 

 of the Theriodontia, Anomodontia, Sauropterygia, the squamosal is the 

 only bone which invests the temporal region. The squamosal of the 

 most primitive reptiles, the Cotylosauria, shows practically the same 

 relations as that of the Stegocephala. In Ichthyosaurs, the squamosal 

 covers the dorsal external surface of the quadrate. In Sphenodon, the 

 supra-temporal has been lost, and the bone which remains is the 

 squamosal, its connection with the parietal being correlated with the 

 disappearance of the supra-temporal. The single bone in the temporal 

 region of Ophidia is the supra-temporal ; there is no squamosal ; croco- 

 diles possess a true squamosal, but no supra-temporal, and so also the 

 Dinosaurs. 



Sternum and Episternum of Mammals. | — L. P. Kravetz has studied 

 the development of the sternum and episternal apparatus in the pig and 

 in Hits musculus. He concludes from these inquiries that the anamnian 

 and amniotan sternum are homologous. The episternal apparatus some- 

 times develops in connection with the sternum and sometimes with the 

 clavicle, and the question of the morphological significance of the 

 episternum of mammals cannot be solved on the ground of development. 



European Hares.J — M. Hilzheimer gives a diagnostic table of these, 

 with notes upon distribution. He enumerates 4 species, embracing 



* Tuft's College Studies, ii. No. 2 (Scientific Series), 1906, pp. 35-73 (4 pis.), 

 t Bull. Soc. Imp. Nat. Sci. Moscou, xix. (1905) pp. 1-59 (2 pis.). 

 % Zool. Anzeig., xxx. (1906) pp. 510-13. 



