THE F'F.TUS. 1047 



forms the pharynx and a'?;ophauu.s ; the posterior infpsfinp, that wives rise to 

 the rectum ; and the middh intestine, which becomes the stomach and in- 

 testines. 



The middle intestine appears at first as a uniform cylindrical tube, the 

 diameter of which is afterwards nioditied to (-(jiistitute the orj^ans comprised 

 between the oesophajj'us and rectum. 



1. Mouth. — It begins by a depression limited by the maxillary buds. This 

 blind pouch gradually enlarues inwardly, and proceeds to meet the pharynx, 

 from which it is only separated, at a certain period, by a thin membrane ; this 

 i.s at last absorbed, and the two cavities then communicate. Until tlie third 

 month, the mouth is confounded with the nasal cavities ; at this time the palate 

 appears, and this eventually isolates them. 



2. Tomjue. — Appearing at first as a small prominence on the maxillary 

 buds, the tongue is completed by the addition to it of a bud from the second 

 branchial arch. Its epithelium and glands come from the external blastodermic 

 lamina : they are developed in the third and fourth months. 



'.\. Phari/nx and msophafius. — These two organs become enlarged and 

 elongated as the foetus grows. The oesophagus communicates at first with the 

 trachea ; but it slowly closes, and finally separates completely from that canal. 



4. Stomach. — This is formed by the dilatation of the anterior part of the 

 middle intestine. The dilatation is fusiform, and its largest axis longitudinal ; 

 it soon incurvates, and its longest axis is then transversal. In Ruminants, the 

 stomach is at its first appearance simple ; but before long it shows grooves on 

 its surface, and in its interior septa, as in the normal state. During foetal life 

 this organ is small ; but after birth, when solid food begins to be taken, it 

 augments rapidly in volume. During lactation in Ruminants, there is remarked 

 a predominance of the fourth over the other gastric compartments ; but im- 

 mediately the young animal commences to consume fibrous aliment, the rumen 

 (juickly increases in size, and it is not long before it becomes the most consider- 

 able division. 



5. I/)tfsfines. — The intestinal tube is primarily of a uniform calibre, though 

 in a short time there can be distinguished the various regions of which it is 

 composed. According to A. Baer, the caecum is early seen in hoofed animals, 

 and is situated in the vicinity of the omphalo-mesenteric duct. This duct 

 detaches itself from the extremity of an intestinal loop, which is drawn towards 

 the umbilical ring ; when the latter is becoming atrophied and progressing 

 towards complete obliteration, this loop reascends into the abdominal cavity. 



The intestines are smooth on their inner face during the first two months ; 

 but during the third they show their villosities and the glands of Lieberkuhn. 

 The Brunnerian and solitary glands are a little later in showing themselves. 



6. Rectum. — This is derived from the posterior intestine, and is developed 

 like the other portions. 



7. Anus. — Towards the caudal extremity of the foetus is observed a depres- 

 sion, analogous to the buccal ci/J-dc-sac. This gradually deepens, and is joined 

 to the rectum and genito-urinary organs. Later, it is separated from the latter, 

 and then belongs exclusively to the alimentary canal. 



B. Annexes of the Alimentary Canal. — These are the salivary glands, 

 teeth, liver, pancreas, and spleen. 



1. Salirar// glands. — These are developed in a solid cellular bud, which is 

 related to the epithelium at the commencement of the digestive apparatus. This 



