Striated circular fibres are distinct at 120 mm. It is probable that these are “a further differentiation of smooth muscle” (McGill). The development of the striated muscle of the human oesophagus has not been satisfactorily studied. The oesophageal smooth muscle layers at first extend to the larynx, where they contrast sharply with the striated fibres of the inferior pharyngeal constrictor. There is no evidence of a downgrowth of these fibres upon the oesophagus.
They may blend with the hepatic trabecular at one or both ends. These detached ducts are lined with regular cuboidal or columnar epithelium and may show a clear-cut lumen. Such ducts were noted in embryos measuring 8, 9.4, and 10.2 mm., and, according to Elze (1907), in those of 7 and 11 mm.
237 there is externally, on either side of the cesophagus, an oblique depression in the epithelium with a corresponding internal elevation. It is so situated that if the walls of the cesophagus should coalesce along this groove a ventral portion would be cut off, communicating freely with the trachea near its bifurcation.
D. ph.-br. Ill, ductus pharyngobranchialis of the third pharyngeal pouch; D.
This membrane is clearly shown in an embryo 2.15 mm. long, as figured by His (Fig. 235, A). The digestive tract at this stage has no anterior opening.
Anat. und Entw. Suppl.-Bd., S. 403-434.
Keibel and Elze have shown that it usually disappears at about this stage, but they found remnants of it in one specimen measuring 11.5 mm. Embryo of 7.5 mm.
– The digestive tract of an embryo of 4.9 mm., shown in median sagittal section. X24 diam.
There is still no external opening. The caudal intestine, which in Ingalls ‘s specimen had a wide lumen, is reduced to a strand of cells.
313 has been described by Pearce. In a 54 mm. embryo he found them represented by small groups of from ten to fifteen cells, directly connected with the sides of the ducts.
Human Immunodeficiency Virus (HIV)/Acquired Immune Deficiency Syndrome (AIDS) HIV is a v irus t hat attacks t he white blood cells, causing a n immune deficiency and leaving the body susceptible to opportunistic infections and cancers. AIDS is the name of this syndrome. By the end of 2002, nearly 900,000 cases w ere r eported i n t he United S tates, a nd A IDS wa s t he s econd m ost common c ause o f de ath i n i ndividuals be tween 25 a nd 4 4 ( Cotran, R .S., Kumar V., a nd C ollins, T., 20 03).
The islands in an embryo of 99 mm. (Fig. 313, b) already resemble those of the adult. In sections stained with haematoxylin and eosin, they appear as pale areas, composed of anastomosing solid cords or rows of cells.