- Amphicoelous; parietals separate; clavicles dilated and with a perforation near the ventral end.
The gill-slits may be stated briefly as follows: - (a) the presence of two kinds of branchial bars in all species and also of small cross bars (synapticula) in many species; (s) numerous gill slits, from forty to more 1 - _ than a hundred pairs; (y) the addition of new gill-slits by fresh perforation at the posterior end of the pharynx throughout life.
A large number of mammals possess a perforation, or foramen, on the inner side of the lower end of the humerus, and also a projection on the shaft of the femur known as the third trochanter.
The vertebrae of the neck unite by nearly flat surfaces, the humerus has lost the foramen, or perforation, at the lower end, and the third trochanter to the femur may also be wanting.
Thecurrent being alternately transmitted and shut off, as a hole passes on and off the aperture of the tube or bellows, causes a vibratory motion of the air, whose frequency depends on the number of times per second that a perforation passes the mouth of the tube.
Here the merit of nickel steel is not so much that it resists perforation, as that it does not crack even when deeply penetrated by a projectile.
The perforation of the paper when done by hand is usually performed by means of small mallets, but at the central telegraph office in London, and at other large offices, the keys are only used for opening air-valves, the actual punching being done by pneumatic pressure.
The end wall is usually very thin, and the protoplasm on artificial contraction commonly sticks to it just as in a sieve-tube, though no perforation of the wall has been found.
The larval period commences at about the thirty-sixth hour with the perforation of the mouth, first gill-cleft and anus.
The effects of the ingestion of large quantities may be so rapid that death may take place in a couple of hours, owing to collapse, consequent on perforation of the walls of the oesophagus or stomach, or from asphyxia due to swelling of the glottis consequent on some of the acid having entered the larynx.
Submucous haemorrhages are usually present, but perforation is rare.
Ornatus), distinguished from all the rest by the presence of a perforation in the lower end of the humerus, and hence sometimes separated as Tremarctus.