734 



SOLIPEDA. 



. 508. 



four years ; four teeth have been shed and renewed. 

 (Aftsr Youatt.} 



Fie. 509. 



Five years ; all tlie incisors have been shed and re- 

 newed; the middle pair much worn. {After 

 Youatt.} 



ally obliterated in the first, or mid-incisors, 

 at the sixth year ; in the second incisors at 

 the seventh year, and in the third, or outer 

 incisors, in the eighth year, in the lower jaw. 

 It remains longer in those of the upper jaw, 

 and in both the place of the " mark " con- 

 tinues for some years to be indicated by the 

 dark-coloured cement, even to about sixteen 

 years old. At this period the worn summits 

 of the incisors present a subtriangular form. 



The canine teeth are small in the horse, 

 and rudimentary in the mare ; the unworn 

 crown is remarkable for the folding in of the 

 anterior and posterior margins of enamel, 

 which here includes an extremely thin layer 

 of dentine. The representative of the first 

 premolar in the first set of teeth is a very 

 small and simple rudiment, and is soon shed. 

 The three normal premolars are as large and 

 complex as the true molars, the anterior one 

 being usually the largest of the series in the 

 upper jaw. 



Salivary Glands. The salivary apparatus 

 in the Solipeda is very extensive, perhaps more 



so than in any other class of quadrupeds, con- 

 sisting of large glandular masses divided into 

 numerous lobes and lobules of a pale colour, 

 and but loosely connected together by cellular 

 tissue. 



The Parotid Glands in the horse constitute 

 a secreting apparatus, the bulk of which is 

 extremely remarkable. Each of these glands 

 extends from the external meatus auditoreus 

 along the side of the head and of the lower 

 jaw, as far forwards as the masseter muscle, 

 and at the same time stretching deeply in- 

 wards as far as the side of the trachea. This 

 enormous glandular organ may be considered 

 as composed of three principal portions : each 

 furnishing its excretory duct, which, however, 

 soon unite to form a common canal, which at 

 first descends within the angle of the jaw, 

 whence, winding round the anterior edge of 

 the masseter, it mounts up externally as far as 

 the buccinator muscle, which it perforates 

 nearly opposite the fourth molar tooth of the 

 upper jaw, its internal orifice being situated 

 in the centre of a prominent papilla. 



The Submaxillary Glands are much smaller 

 than the parotids. Posteriorly they consist 

 of a thick globular portion, which is adherent 

 to the inner surface of the parotid, but as 

 they advance forwards, they become consider- 

 ably attenuated, each terminating in its appro- 

 priate duct. The latter is of considerable 

 length, and, after passing the sublingual gland, 

 with which it contracts some attachments, 

 opens into the mouth at a little distance be- 

 hind the canine tooth, its opening being in 

 the immediate vicinity of a papilla that seems 

 to form a kind of valve at its orifice. 



The Sublingual Glands are smaller than the 

 preceding, and are of an oblong shape : they 

 pour the saliva that they secrete intp the 

 cavity of the mouth through numerous orifices 

 arranged in several rows on each side of the 

 tongue. 



In addition to the above large glandular 

 organs, there remain to be noticed the Molar 

 Glands, consisting of numerous detached granu- 

 lar-looking bodies of a lenticular shape situated 

 beneath the mucous membrane that lines the 

 buccinator muscle, and the inner surface of 

 the superior maxillary bone behind which they 

 mount up into the zygomatic fossa to within 

 a little distance of the abductor muscle of the 

 eye. 



Pharynx. The . pharynx in quadrupeds 

 generally presents a structure very similar to 

 that of the human race, and may be said to be 

 composed of analogous muscles : nevertheless 

 its horizontal position in these animals renders 

 the necessity for muscular exertion during 

 deglutition greater than in man ; and, accord- 

 ingly, these fibres are not only stronger in 

 quadrupeds than in our own persons, but 

 sometimes additional muscles are met with, 

 by the aid of which the action of swallowing 

 is facilitated. 



In the horse, the muscle which represents 

 the middle constrictor of the pharynx might 

 more properly be called the pterygo-palato- 



