AVKS. 



300 



in consequence of the connections of the ossi- 

 culuin, is a tensor, and draws the membrana 

 tympani outwards. It is counteracted by two 

 small tendinous cords that are extended to the 

 internal parietes of the tympanum. 



The labyrinth of the ear of birds consists 

 of the vestibule, the three semicircular canals, 

 and the rudiment of the cochlea. These parts 

 are included within the bones of the cranium, 

 which form a dense vibraiile case (d) around 

 the whole internal ear. 



The vestibule is small in proportion to the 

 other parts, but is more elongated than in the 

 cold-blooded Reptilia. 



The semicircular canals have been termed 

 by Scarpa, from their gradation in bulk, 

 caiuiles major, minor, and minimus. The 

 largest is most superior, and has a vertical 

 position* (h, fig. 141). The smallest is situ- 

 ated horizontally (k,k). The canalis minor 

 or second canal (i) is vertical, it ascends upon 

 the horizontal canal, and opens into its side 

 at m. They contain corresponding tubes of 

 vascular membrane, and they also possess en- 

 larged ampulla, 1 (/), on which the nerves are 

 distributed in the same manner as in mam- 

 malia. 



The place of the cochlea is supplied by a 

 short obtuse osseous conical tube (n, fig. 141), 

 as in the Crocodile, very slightly bent, with 

 the concavity directed backwards. Its interior 

 is occupied by two small cylinders of fine car- 

 tilage, each a little twisted, and united by a thin 

 membrane at their origin and termination. They 

 proceed from the osseous bar, which separates 

 the two foramina, corresponding to the foramen 

 ovale and rotundum. The sulcus, which is left 

 between the cartilages, is dilated near the point, 

 and accommodates the same branch of the 

 auditory nerve, which is sent to the cochlea in 

 mammalia. This nerve spreads in fine fila- 

 ments upon the united extremity of the carti- 

 laginous cylinders. The tube is divided by 

 the presence of the cartilages into two scala?, 

 the anterior of which communicates with the 

 vestibule and is not closed ; the posterior scala 

 is shorter, and communicates with the tym- 

 panum by the foramen rotundum, which is 

 closed by a membrane. Besides these parts the 

 cochlea still contains a trace of the cretaceous 

 substance which forms so conspicuous a part 

 of the organization of the internal ear in 

 Fishes. 



The Struthious birds manifest their close 

 relation to the Reptilia by having the tube 

 corresponding to the cochlea, very small in 

 proportion to the other parts. 



The seventh cerebral nerve is received into 

 a fossa, and there divides into five branches ; 

 one is the facial, or portio dura, and the others 

 are sent to the semicircular canals and the tube. 

 The facial nerve receives a filament from the 

 par vagum, which traverses the ear, and is 

 afterwards distributed to the palate. 



Comparetti has described two canals leading 



* In the Insessores this canal is generally the 

 smallest of the three. 



from the labyrinth of birds, which correspond 

 with the aqueducts of the mammalia.* 



Organ of Smell. The close affinity subsist- 

 ing between the cold and warm-blooded ovi para 

 is no where more strongly manifested than in 

 the olfactory organs. The external nostrils are 

 simple perforations, having no moveable car- 

 tilages or muscles provided for dilating or con- 

 tracting their apertures, as in mammalia. The 

 extent of surface of the pituitary membrane 

 is not increased by any large accessory cavities, 

 but simply by the projections and folds of the 

 turbinated bones. The olfactory nerve is sim- 

 ple, as in the Tortoise, and passes out of 

 the skull, as before observed, by a single fo- 

 ramen. 



The external nostrils vary remarkably both 

 in shape and position, and serve on that ac- 

 count as zoological characters. They are placed 

 at the sides of the upper mandible in the 

 majority of birds, but in some species are 

 situated at or above the base of the bill; the 

 latter is the case in the Toucans; in the Ap- 

 teryx Australis they are found at the extremity 

 of the long upper mandible. 



In general they are wide and freely open to 

 facilitate the inhalation of air during the rapid 

 motions of the bird, but sometimes they are 

 so narrow that, as in the Herons, they will 

 scarcely admit the point of a pin ; and in ihe 

 Gannet they have been supposed, but erro- 

 neously, to be wanting altogether .f 



In the Rasores the nostrils are partially 

 defended by a scale. In the Corvuta they 

 are protected by a bunch of stiff feathers 

 directed forwards. In the Petrels the nostrils 

 are produced in a tubular form, parallel to one 

 another for a short distance along the upper 

 part of the mandible, with the orifices turned 

 forwards (a, Jig. 142.) 



The septum narium is, in general, complete, 

 and is partly osseous, partly cartilaginous. It 

 is perforated in the Swan just opposite the 

 external nostrils. The surface of the septum 

 is very irregular in this bird, and the pituitary 

 membrane which covers it is highly vascular. 



The outer side of each of the nasal passages 

 gives attachment to three turbinated laminae. 

 The inferior one is a simple fold adhering to 

 the septum narium as well as to the side of the 

 nose; the middle one is cartilaginous and is 

 the largest. It is of an infundibular figure, 

 and adheres by its base to the septum of the 

 nose, and externally to the cartilaginous ala or 

 side of the nostril. It is convoluted with two 

 turns and a half in the Anserine Birds, but 

 in the Grallatores it is compressed and forms 

 only one turn and a half. The superior tur- 

 binated lamina (m m, fig. 140) generally 

 presents the form of a bell ; it is also cartila- 

 ginous, and adheres to the ethmoidal and 

 lachrymal bones. It is hollow, and divided 

 into two compartments, which are prolonged 

 in a tubular form ; the internal one extends to 



* See Cuvier, Logons d'Anat. Coinp. torn, ii., 

 and Macartney in Hccs' Cyclopaedia, Art. Birds. 

 t See Montague's Ornithological Dictionary. 



