THE NASAL CAVITY 



71 



middle fossae. The middle fossa (Fossa cranii media) is the widest part of the 

 cavity. It extends backward to the internal sphenooccipital and petrosal crests, 

 thus corresponding to the post-sphenoid. In its middle is a small fossa, the sella 

 turcica, in wliich the pituitary body, or hypophysis cerebri, is situated. On either 

 side are two grooves for nerves; the inner one transmits the ophthalmic, third, 

 and sixth nerves to the foramen lacerum orbitale; the outer one leads to the foramen 

 rotundum, and lodges the maxillary nerve. External to the grooves is a depression 

 for the pyriform lobe of the cerebrum. The posterior fossa (Fossa cranii posterior) 

 corresponds to the basilar part of the occipital bone. It contains the medulla, 

 pons, and cerebellum. In front is a median depression (Fossa pontis) for the pons. 

 The surface behind this is concave transversely and slopes gently downward to the 

 foramen magnum; it supports the medulla. On either side are th(^ foramen 

 lacerum basis cranii and the hypoglossal foramen. 



The anterior or nasal wall is formed by the cribriform plate of the ethmoid, 

 which separates the cranium from the nasal cavity. It is perforated by numerous 

 foramina for the passage of the olfactory nerve-bundles. 



Fig. 36. — Medi.w Section of Skull of Horse Without the M.\.vdible. 

 The septum nasi is removed, but the mucous membrane on the turbinal bones is retained. a, a', Superior 

 turbinal bone, dotted line indicating limit between anterior coiled part and posterior uncoiled part; b, b', .superior 

 turbinal folds, inclosing bars of cartilage; c, fold of mucous membrane formed by union of 6 and 6'; d, d', anterior 

 coiled and posterior uncoiled part of inferior turbinal, dotted line indicating septum between them; e, f, inferior 

 turbinal folds, former (alar fold) inclosing bar of cartilage; g, h, i, .superior, middle, inferior meatus; o, o', frontal 

 sinus; partial septum between o and «'; q, nasal part of frontal sinus (nasal sinus); r, lateral mass of ethmoid 

 bone; s, sphenoidal sinus; t, cranial cavity; ti, opening made in superior turbinal bone at point where drainage 

 of frontal sinus maj- be obtained. (After EUenberger, in Leisering's Atlas.) 



THE NASAL CAVITY 



The nasal cavity (Cavum nasi) is a longitudinal passage which extends through 

 the ui)pcr part of the face. It is divided into right and left halves ])y a median 

 septum nasi. The lateral walls are formed by the maxilla, premaxilla, and the 

 perpendicular part of the palate bones. Attached to them are the turbinal bones, 

 which subdivide each nasal fossa into three meatuses (Meatus nasi). This wall 

 is crossed obliquely by the canal and groove for the naso-lacrimal duct, and its 

 posterior part is perforated by the spheno-palatine foramen. The superior wall 

 or roof is formed by the frontal and nasal ])ones. It is concave from side to side, 

 and nearly straight longitudinally, except in the posterior part, where it curves 

 downward. It presents a median elevation, the nasal crest. The inferior wall 

 or floor is formed by the palatine processes of the premaxilla:; and maxilhv, and the 

 horizontal parts of the palate bones. It is wider but consideral)ly shorter than the 

 roof. It is concave transversely, and nearly horizontal from before backward, 

 except in the posterior third, where there is a slight declivity. The anterior part 

 presents a mecUan groove for the cartilaginous septum, and a furrow for the organ 

 of Jacobson on either .side. On either side of the palatine processes of the premax- 

 illae is the palatine cleft. 



