394 DIGESTIVE SYSTEM OF THE HORSE 
forward and upward, and for the most part turn toward the median plane of the 
dorsum of the tongue. Its action is to retract and depress the tongue.! 
3. Genio-glossus.— This is a fan-shaped muscle, which lies parallel to the me- 
dian plane of the tongue. It is separated from the muscle of the opposite side by a 
layer of fat and areolar tissue. It arises from the medial surface of the ramus 
of the mandible just behind the symphysis. From the tendon the fibers pass in 
a radiating manner, some curving forward to the tip, others pass toward the dorsum, 
and others toward the root of the tongue; some fibers pass from the posterior end 
of the tendon to the body and small cornu of the hyoid bone. The muscle as a 
whole is a depressor of the tongue, and especially of its middle portion; when both 
muscles act, a median groove is formed on the dorsum. The posterior fibers pro- 
trude the tongue, the middle fibers depress the tongue, and the anterior fibers 
retract the tip of the tongue. 
In some cases there is a small anomalous muscle which arises by a delicate tendon with the 
genio-glossus and is attached behind with the genio-hyoideus. 
Vessels and Nerves.—The arteries of the tongue are the lingual and sub- 
lmgual branches of the external maxillary artery. The veins go to the internal 
and external maxillary veins. The lymph vessels go chiefly to the pharyngeal 
lymph glands. The sensory nerves are the lmgual and glosso-pharyngeal, and the 
muscles are innervated by the hypoglossal nerve. 
THE TEETH IN GENERAL 
The teeth are hard white or yellowish-white structures implanted in the alveoli 
of the bones of the jaws. Morphologically they are large calcified papillae. Fune- 
tionally they are organs of prehension and mastication, and may serve as weapons. 
The domesticated mammals have two sets of teeth. The teeth of the first set 
appear during early life and are known as deciduous or temporary teeth (Dentes 
decidui),? since they are replaced during the period of growth by the permanent 
teeth (Dentes permanentes). They are classified according to form and position 
as follows: 
1. The incisor teeth (Dentes incisivi) are situated in front and are implanted 
in the premaxilla and mandible. 
2. The canine teeth (Dentes canini) are situated a little further back, and 
interrupt the interalveolar space. 
3. The premolar and molar teeth (Dentes premolares et molares) form the 
sides of the dental arch. The premolars form the anterior part of the series; they 
appear in both sets. The molars appear only in the permanent dentition. The 
term cheek teeth is used to include both premolars and molars. 
The interval between the incisors and premolars is the interalveolar or inter- 
dental space. 
As the teeth of the two sides of the jaw are alike in number and character 
(in normal cases), the complete dentition may be briefly indicated by a dental 
formula such as the following: 
2(1 
In this formula the letters indicate the kinds of teeth, and the figures above and 
below the lines give the number of teeth of one side in the upper and lower jaw 
respectively in man. 
1 
C-P 
M - 
1 3 
ew) 
wo | w 
ll 
oo 
we 
bol bo 
‘It may be possible to recognize in this muscle three parts, which would correspond to 
the baseo-, kerato-, and chondro-glossus of man. 
2 They are also popularly spoken of as “milk” teeth. 
