850 THE NERVOUS SYSTEM OF THE DOG 



9. The cruciate fissure is the deepest and most characteristic. It cuts deeply into the an- 

 terior third of the dorso-medial border and runs ahnost straight outward. It is continuous on the 

 medial surface of the hemisphere with the caUoso-marginal or splenial fissure. 



10. The sulcus rhinalis is continued on the tentorial 

 surface of the hemisphere by the occipito-temporal fissure. 

 Anteriorly it is prolonged as the olfactory fissure, which 

 is concealed by the olfactory bulb and tract . . 



11. The calloso-marginal fissure usually consists of 

 two parts, splenial and genual. The splenial fissure is 

 parallel with the splenium and middle part of the corpus 

 oaUosum on the medial surface of the hemisphere. It is 

 continuous in front with the cruciate fissure and runs for- 

 ward and outward across the tentorial surface to join the 

 occipito-temporal or calcarine fissure. It gives off from 



Fig. esi.-RiGHT Cereebal Hemisphere ^ts highest part the short accessory cruciate fissure. The 

 or Dog- .Medial View genual fissure IS approximately parallel with the genu of 



the corpus callosum. 

 i,Corpu.scallosum; 2', genu; i , splen- -^2^ The suprasplenial fissure runs ahnost parallel 



ium of corpus callosum; a. genual fissure; ^-^j^ ^j^g posterior part of the caUoso-marginal fissure on 

 6, splenial fissure; c, suprasplenial fissure; ^[^g ^^^^^ ^^^ tentorial surfates of the hemisphere. 

 d. hippocampal fissure; e, sulcus corporis j^g -pj^g occipito-temporal or calcarine fissure is the 



callosi; /, postsplemal fissure; g. lesser continuation on the tentorial surface of the hemisphere of 

 cruciate fissure; h, cruciate fissure. (After ^j^g gplgnial fissure. 

 Ellenberger, in Leisenng's Atlas.) ^^ rpj^g hippocampal fissure forms the medial 



boundary of the piriform lobe. 



The olfactory bulb is large and is compressed laterally; its anterior end pro- 

 jects beyond the frontal pole of the hemisphere. The tract is short and is also 

 flattened laterally. Both contain a narrow cavity vi^hich communicates with the 

 lateral ventricle. The pirifomi lobe is large and rounded. 



The cranial nerves present the following special features which are worthy of 

 notice : 



The ophthalmic nerve gives off frontal, long ciliary, ethmoidal, and infratro- 

 chlear branches. The lacrimal nerve arises from the ophthalmic at its origin ;'^ its 

 recurrent branch emerges at the orbital ligament and concurs with the zygomatic 

 and frontal nerves in the formation of the anterior auricular plexus. The frontal 

 nerve emerges from the orbit in front of the upper end of the orbital ligament, 

 ramifies in the upper lid and the adjacent skin of the forehead, and sends branches 

 backward to the anterior auricular plexus. The long ciliary nerve accompanies 

 the optic nerve and divides into several branches which pierce the posterior part of 

 the sclera. The ethmoidal nerve gives off internal nasal branches and ends in the 

 muzzle. The infratrochlear nerve runs forward between the medial straight and 

 the superior oblique muscles of the eye and ramifies on the face in the vicinity of 

 the medial canthus. 



The maxillary nerve emerges through the foramen rotundum and gives off 

 five branches. The lacrimal nerve emerges from the orbit lateral to the frontal; 

 its branches concur with the frontal and auriculo-palpebral nerves in the formation 

 of the anterior auricular plexus. The zygomatic nerve emerges through an opening 

 in the upper part of the orbital ligament and ramifies in the lower lid and on the 

 adjacent surface of the face. The infraorbital nerves, two in number, divide within 

 the infraorbital canal and after their emergence upon the face, thus forming seven 

 or eight external nasal and superior labial branches. The sphenopalatine nerve 

 gives off lesser and greater palatine and posterior nasal nerves. 



The mandibular nerve passes out through the foramen ovale. The superficial 

 temporal nerve divides into auricular, temporal, and malar branches; the last- 

 named crosses the masseter and ramifies with the buccal nerves. The mylo-hyoid 

 nerve is given off from the mandibular nerve almost immediately after the latter 

 emerges from the cranium; it innervates the mylo-hyoideus and occipito-mandib- 

 ularis and gives off a branch which turns around the lower jaw, joins the inferior 



' The origin of the lacrimal nerve is such that EUenberger-Baum and Martin describe it 

 as a branch of the maxillary nerve. 



