_1_, Corpus callosum; _1′_, genu, _1″_, splenium of corpus callosum;
_a_, genual fissure; _b_, splenial fissure; _c_, suprasplenial
fissure; _d_, hippocampal fissure; _e_, sulcus corporis callosi;
_f_, postsplenial fissure; _g_, lesser cruciate fissure; _h_,
cruciate fissure. (After Ellenberger, in Leisering’s Atlas.)
]
5. The =coronal fissure= is the continuation of the ectomarginal. It
runs forward and downward, curving around the cruciate fissure, and ends
behind the middle of the presylvian fissure.
6. The =ectolateral fissure= lies between the posterior part of the
ectomarginal fissure and the suprasylvian fissure.
7. The =entomarginal fissure= lies between the anterior part of the
ectomarginal fissure and the dorso-medial border. It is often indistinct
and not rarely absent.
8. The =presylvian fissure= begins at the sulcus rhinalis, a little in
front of its middle, and curves over the anterior third of the lateral
surface of the hemisphere in front of the coronal fissure.
9. The =cruciate fissure= is the deepest and most characteristic. It
cuts deeply into the anterior third of the dorso-medial border and runs
almost straight outward. It is continuous on the inner surface of the
hemisphere with the calloso-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.
[Illustration:
FIG. 545.—DEEP DISSECTION OF HEAD OF DOG, SHOWING ESPECIALLY
TRIGEMINAL AND HYPOGLOSSAL NERVES.
_a_, Hypoglossal nerve; _b_, cervical branch of _a_; _c_, mandibular
division of trigeminus; _d_, lingual nerve; _e_, nerve to
submaxillary gland; _f_, deep temporal nerve; _g_, pterygoid nerve;
_h_, buccinator nerve (cut); _i_, inferior alveolar or dental nerve;
_k_, staphyline branch of lingual nerve; _l_, chorda tympani; _m_,
mylo-hyoid nerve; _n_, sphenopalatine nerve; _o_, lesser palatine
nerve; _p_, great palatine nerve; _q_, infraorbital nerves; _r_,
subcutaneus malæ; _s_, branch of oculomotor nerve to inferior
oblique muscle; _t_, lacrimal nerve; _u_, frontal nerve; _v_,
trochlear nerve; _w_, abducens; _1_, carotid artery; _2_, lingual
artery; _3_, internal maxillary artery; _4_, thyro-pharyngeus
muscle; _5_, hyo-pharyngeus muscle; _6_, thyro-hyoideus; _7_,
sterno-hyoideus; _8_, baseo-glossus. _9_, genio-hyoideus; _10_,
genio-glossus; _11_, stylo-glossus; _12_, pterygoideus internus;
_13_, outline of submaxillary gland (dotted); _14_, atlas; _15_,
bulba ossea; _16_, zygomatic arch (dotted); _17_, rectus oculi
inferior; _18_, obliquus oculi inferior. (Ellenberger-Baum, Anat. d.
Hundes.)
]
11. The =calloso-marginal= or =splenial fissure= is parallel with the
splenium and middle part of the corpus callosum on the inner surface of
the hemisphere. It is continuous in front with the cruciate fissure and
runs downward and outward across the tentorial surface to join the
occipito-temporal fissure and sulcus rhinalis. It gives off from its
highest part the short lesser or accessory cruciate fissure.
12. The =suprasplenial fissure= runs almost parallel with the posterior
part of the calloso-marginal fissure on the inner and tentorial surfaces
of the hemisphere.
The =olfactory bulb= is large and is strongly compressed laterally; its
anterior end projects beyond the frontal pole of the hemisphere. The
tract is short and is also flattened laterally. Both contain a narrow
cavity which communicates with the lateral ventricle. The =pyriform
lobe= is large and rounded.
The =cranial nerves= present the following special features which are
worthy of notice:
The =ophthalmic nerve= gives off lacrimal, frontal, long ciliary,
ethmoidal, and infratrochlear branches. The =lacrimal nerve= arises from
the ophthalmic at its origin;[215] 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 internal
straight and the superior oblique muscles of the eye and ramifies on the
face in the vicinity of the inner canthus.
[Illustration: