MAMMALS 501 



enveloping the muscles and extending forwards to the level of the 

 equator of the globe : its main exit channels are into the posterior and 

 deep facial veins, the external and internal maxillary veins, and the 

 vertebral vein (Davis, 1929). 



The orbital nerves throughout the Placentals conform to the same 

 general plan. The branches of the first division of the trigeminal serve 

 as the sensory supply ; the sympathetic is vasomotor and innervates 

 the smooth orbital muscle ; while the muscles are supplied by the 

 Ilird, IVth and Vlth cranial nerves as in man except that the last 

 nerve supplies the retractor bulbi muscle and the muscles controlling 

 the nictitating membrane when these are j) resent. 



The CILIARY (orbital) ganglion is of interest. It is variable in nature 

 but is always primarily associated with the Ilird nerve. In the lower Fishes 

 (Selachians, etc.) it is represented by groups of cells scattered along this nerve 

 (H. Schneider, 1881 ; Pitzorno, 1913) ; in Teleosteans, Amphibians and 

 Reptiles the ganglion becomes a specific entity associated with this nerve, usually 

 without connection with the Vth or synijDathetic (Schwalbe, 1879). In Birds 

 it has a short root from the Ilird nerve and a slender long root from the trigeminal 

 (Lenhossek, 1911 ; Carpenter, 1911). Langendorff (1900) and Lodato (1900) 

 were unable to confirm the nicotine reaction for the motor fibres in Birds ; it 

 thus appears that physiologically as well as anatomically the cells in these 

 animals are cerebro-sjainal in type. It will be remembered that the ciliary 

 muscle of Birds is striated. In Mammals, although it is small in Equidse (Mobilio, 

 1912), the ciliary ganglion is always present, and in them the connection with 

 the Ilird nerve is always retained (Schwalbe, 1879.; Peschel, 1893 ; Apolant, 

 1896). In many of them the root from the Vth nerve is absent, and frequently, 

 when it is present, it conducts fibres of passage which are not relayed (Antonelli, 

 1890 ; Michel, 1894). The sympathetic root is more frequently absent ; and 

 both of these roots may be absent in man. Among Mammals the ciliary ganglion 

 is often rejaresented by more than, one group of cells. ^ It is probable that in 

 many cases some of these different colonies of cells represent outgrowths of 

 III and others outgrowths of V. When the ganglion is painted with nicotine 

 the motor path is blocked, showing that this is mediated by cell-stations of the 

 autonomic type (Langley and Anderson, 1892), while the sensitivity of the 

 cornea remains unimi^aired, showing that the sensory fibres are relayed in cell- 

 stations which (if present) are of the cerebro -spinal type. 



The ocular adnexa of aquatic Placentals deserve a sjjecial note. 

 Some are only partially adapted to this medium. In the liippopotamus 

 the orbits (like the nose) are elevated so that the eyes are readily kept 

 above the water-level, the lids form a ring rather than a slit-shaped 

 palpebral aperture, the lashes are sparse, and naso -lacrimal canals are 

 lacking. In the Pinnipedes (seals and walruses) the orbits are also 

 directed somewhat ujd wards, there are no tarsal glands, the lacrimal 

 glands (although large in the foetus) are small in the adult and the 

 harderian glands are enormously developed, secreting an abundance of 



1 Ox, Muck (1815) ; rabbit, d'Erchia (1895), Mobilio (1912) ; pig, Antonelli (1890). 



