76 MR. L. T. HOGBEX ON THE 



it runs back beneath the z^'^goiuatic process as far as the glenoid 

 cavity in tlie formation of which it takes a small share." 



There is little to add to accounts previously given relating to 

 the jugal arch in the Sirenia and Cetacea. in the Sirenia the 

 arch is massive, particidarly in Manatus, and the jugal curves 

 deeply downwards in Hcdicore. The malar sufiers little displace- 

 ment on account of the maxilla and it extends postero-ventrally 

 near the glenoid. In Manatas the jugal almost meets the frontal 

 behind the orbit. In the Cetacea the jugal joins the lacrymal 

 Avhen the latter is present ; and the separation of the orbit from 

 the temporal fossa is achieved as in the Equidte by the union of 

 the squamosal with the frontal. 



AVinge*, in his recent revision of the Insectivora, lays stress on 

 the early separation of the Dermoptera, Cladobatidas, and Macro- 

 scelidaj from the other families of the order ; but again overlooks 

 the morphological value of the zygomatic arch. Por nothing 

 more emphatically distinguishes the Tupaiidaj (Cladobatida?, 

 Winge) and Macroscelidaj than the relations of the jugal. In all 

 the remaining families it is greatly i-educed, so that the arch is 

 frequently incomplete owing to its total suppression as in the 

 Soricidfe, Oentetidje, Solenodontidae, and Potamogalida?. In the 

 Erinaceidse, Talpidee, and Chrysochloiidfe, it is present as a slender 

 element inserted in the middle of the arch between the zygomatic 

 processes of the maxilla and squamosal ; never does it join with 

 the lacrymal. In marked contrast, on the other hand, the relations 

 of the jugal in the Tupaiidaj and the Macroscelidas are essentially 

 similar to the condition characteristic of the Metatheria, Hyrax, 

 and certain Rodents : that is, it extends back to the glenoid 

 venti'ally and reaches forward to meet the lacrynjal on the 

 anterior border of the orbit. In the aberrant genus Galeopithecits 

 the jugal is even more powerful and contributes a large share 

 in the formation of the glenoid cavity. 



In the Chiroptera the zygomatic arch is complete ; but the role 

 of the jugal is greatly restricted, as in the Erinaceidas. The 

 maxilla displaces the jugal, not as is usually the case on the 

 ventral side, but dorsally ; and sometimes comes into contact with 

 the squamosal element on the upper border of the arch. 



The enclosure of the eye-socket, which has been independently 

 efiected in certain of the more specialized members of other ordei's, 

 has become a fixed character in the Primates through the union of 

 the postorbital process of the jugal" with the frontal, so that the 

 formei' has acquired a new role. The jugal does not usually 

 extend far behind its junction with the frontal in the Lemurs and 

 in the Anthropoidea ; but in certain genera of the Prosimias it 

 may extend back to the glenoid, as e. g , Chiro»ii/s, Indris, and 

 Tarsius. A more rigid distinction — not previously mentioned — 

 between th.e Lemuroidea and the higher Primates than the 

 complete enclosure of the orbit by the ingrowth of the jugal to 



* Winge. " Udsigt over lusektaudei'iies iudbyrdes Slaegskab." Vidensk. Meddel. 

 f. Dausk Naturhist. Foreiiiiig Kjobeuhavn, 68. 1917. 



