Objectives:

E. Lens

At the other end of the eye is the retinal layer. The preservation is not that great, but you can with some work find the 10 layers (use plate 126-2). The hardest layers to identify are the very thin external limiting membrane and the internal limiting membrane (which is easier because it is on the surface). The lamina vitrea you will not be able to find. Note that the band of densly packed nuclei just inside of the external limiting membrane are the nuclei of rods and cones (called the outer nuclear layer). Just inside of this is another layer of less densly packed nuclei, and this is the inner nuclear layer. It consists of 4 cells types. The thinnest nuclear layer consists of fewer, larger nuclei is a ganglion layer. (see pages 762-763 for more of this).

The iris is also visible in this section. It can be identified by the dark staining granules. It has curled up on itself.
 

166B Retina
This retina slide is not as good as the others. The 3 nuclear layers (inner, outer and ganglion) are visible but the staining is too faint for all 10 layers to be visible.
 

164B Eye monkey, general structure

There are only three of these slides, but they are the best ones in the set. They have all the structures of 164a but have also the lens as well as better preservation. Most of the structures shown in Plate 127 can be seen in the iris of this slide. The abbreviated labeling on the above picture corresponds to that used in the Atlas. The retina is well preserved and only the external limiting membrane is difficult to see. Easy to locate is the circular layer of smooth muscle which is located at the tip of the iris (the inner most part). The ciliary muscle can be found at the other end of the iris.

At the corneal side of the eye, the corneal epithelium and endothelium are quite well preserved. You will notice in the lens that only the outer layers are continuous. These are lens fibers. The lens epithelium is simple cuboidal but it is different at the margins. The lens fibers have no nucleus except at the lateral margins. Delicate fibers, called zonular fibers can be seen extending between the lens and the surrounding retinal layer.
 
 

166A Optic nerve head

There are two groups of slides of this tissue, one seems to be Mallory-Azan stained, the other H&E stained. The above picture comes from the H&E stained slide. Both slides show the same region given you the Atlas plate 126.

In the Mallory-Azan slide, the external limiting membrane is very clear and most of the 10 layers of the retina can be identified. The pigment epithelium is a thin layer one cell thick. Below it is a thick orange layer called the choroid that blends into a dark layer. Below the dark layer is a blue layer called the sclera. The dark brown material is melanin produced by melanocytes located in the choroid layer. the melanin is so dark that it masks the vasculature present in the choroid.

In the H&E stained slide, the choriod is not so heavily stained and the cellular makeup of the choroid is easer to visualize. However, the 10 retinal layers are not all visible. PM - pia mater, DM - dura mater, AM - arachnoid mater, SubA - subarachnoid space. All are adjacent to the nerve fiber.
 
 
 

169 Lacrimal gland, MA, human

 This is a rather heavily stained slide. However, you can get the impression of a multilobular gland of serous tubuloacini. The lumen of the glands is relatively large in diameter compared with other serous acini such as parotid and pancreas.
 

B. Cristae ampullares

171A Internal ear, cochlea

This slide will challenge you. If you mount the slide with the label on the left, you will see in the upper left hand corner a piece of developing cerebellum. The cochlea is toward the bottom of the slide and consists of several cavities arranged sequentially forming a U. The organ of Corti can be seen in a couple of these. Once you have figured out what an organ of Corti looks like, you can turn your slide around 180° and you can find one that looks exactly like plate 130-2 in your Atlas. The spiral ganglion can be found adjacent to the large open spaces which represent the scala vestibuli (sv), scala tympani (st) and cochlear duct (cd). In the center of the cochlea is the cochlear nerve (Fig. 24.14). The other large opening in this section is apparently a piece of the crista ampularis. The different cell types you should be able to identify using the text and atlas.
 

172A Crista ampullaris  RR&K, page 780, Fig. 24.12

This slide has both crista ampullaris and cochlea in it, but its particular feature is the hillock that forms the cristae. The gelatinous cupula can be seen just above this hillock that consist of sensory hair cells. Refer to Fig. 24.12 for help identifying this feature. The cochlea is also well preserved but the orientation is not as good as in slide 171.

172B Crista ampullaris

This slide is not as good as the previous one. However, you will find several cupola structures in the tissue as well as a nerve fiber. Some of these slides have parts of the cochlea.

171B Cochlea
This is similar to the previous slide except it is moved over closer to the cochlea. It also has crista ampullaris. One of the more interesting things about this slide is the way you can track the nerve fibers through the bony tissue to the sensory receptors and ganglia.
 

173 External ear, monkey

The external ear consists of a central layer of elastic cartilage surrounded by skin structures. We will be covering skin structures in a few weeks but for the time being simply identify the epithelium, underlying connective tissue muscle etc. These skin structures include hair follicles, stratified squamous epithelium, keratinized, sebaceous glands, numerous blood vessels and sometimes peripheral nerves.